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421 email error is typically a temporary routing issue on the receiving mail server's end. These should usually be resolved automatically, and you should receive a final bounce-back message if the message completely fails.

You usually would not receive a bounce-back message for this type of error. If your message is going to be delayed more than 24 hours, then sometimes a "delivery has been delayed" soft bounce will be returned to you, to let you know that the delivery has yet to complete succesfully.

Common variations of the 421 email error

  • 421 4.2.1 : (DYN:T1)
  • 421 4.3.1 Out of disk space for temp file
  • 421 4.3.2 All server ports are busy
  • 421 4.3.2 All server ports are busy
  • 421 4.4.2 Error: timeout exceeded
  • 421 #4.4.5 Too many connections from your host.
  • 421 #4.4.5 Too many connections to this host.
  • 421 4.7.0 Error: too many errors
  • 421 4.7.1 : (DYN:T1)
  • 421 4.7.1 POL-T2 Connection refused
  • 421 4.7.1 POL-T2 Connection refused

  • 421 Downstream server error
  • 421 Fork failed
  • 421 Greylisting enabled, please try later.
  • 421 LDAP verification agent temporarily unavailable: Connection failed
  • 421 out of connection slots
  • 421 Service unavailable - try again later
  • 421 <> Service not available - too busy
  • 421 Server busy, try again later - psmtp
  • 421 service temporarily unavailable
  • 421 Temporary error (#4.3.0)
  • 421 Too many concurrent SMTP connections; please try again later.
  • 421 Unexpected failure, please try later

Resolving a 421 email error

Because errors in the 421 series don't bounceback right away they would be considered a soft bounce. To better understand soft and hard bounces, and general email bounceback errors you can read why does email bounce, bounceback, or error?

Seeing a large amount of 421 email errors in your server's mail logs could be an indication that a lot of your mail users are having difficulties getting their e-mails delivered out successfully on the first attempt.

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n/a Points
2014-05-29 1:56 pm

I keep getting "too many simultaneous connections" for my AOL account. I have a multitude of phones, tablets, and computers that have my AOL account attached. Is there a limit to how many "connections" I can have? If so< what is my next step? If not. how to I remedy this?



9,968 Points
2014-05-29 3:59 pm
Hello Kady, and thanks for your comment.

Are you getting this error just when trying to send email to an AOL email account? This guide itself is on 421 errors, and you would typically see it in a bounce-back message after a message you sent to a AOL user failed to send. In this case you would want to try to send the message again at a later time as the AOL server could be temporarily overloaded.

If you are just getting this error in your mail client, and you are using your AOL account in multiple devices at once, you might be having an issue with IMAP usage on their server.

You might need to stagger the times your different devices check your mail. For instance, have your phone check every 5 minutes, tablets every 7 minutes, first computer every 9 minutes, and so on. You might also want to reduce the total number of messages stored in your main Inbox folder, and archive away messages you don't need to access often. Some email clients will tie up IMAP connections by trying to download lots of old message headers from the server for a message that's older than 30 days and you might not be reading anyways.

Hope that helps, please let us know if you still have any questions at all!

- Jacob

n/a Points
2014-07-31 5:28 am

I am getting 421 error - too many messages? what does that mean. also I am getting a grey pop up box that says do you want to save this password in the list, everytime I send sonmeone an email, what does that mean?I am able to send and receive emails OK, just these annoying two pop up boxes that wont go away. please help

29,167 Points
2014-07-31 9:21 am
This error is typically from the receiving server so it should not be a result of your account. It seems that the receiving server may be getting more mail than it is set to expect, so it is giving the "too many messages" message. You may want to try resending the email again at a later time to see if it will accept it.

Kindest Regards,
Scott M
n/a Points
2014-07-31 10:10 am

this has been happening for about a week now. I send lots of mail and have done for years but I am only getting these error messages for the past week.

the worst pop up box is the grey one that says do you want to save this password in the list, it pops up every two seconds, it is so annoying. i dont know what to do about it.

I am not at all technical and I dont have anyone that can help me :(

11,186 Points
2014-07-31 10:29 am
Are you sending multiple messages in succession to the same email address or to a bulk mailing list?
n/a Points
2014-07-31 10:34 am

different email addresses. similar messages - as I work for a charity and I send membership packs by email. I have been using outlook 2007 to do this for years and only now is it a problem

11,186 Points
2014-07-31 10:38 am
How big is the mailing list? Are you sending them all at once? A specific service provider is most likely seeing a lot of messages coming in to their users and blocking based on that to prevent spam.
n/a Points
2014-08-01 5:55 am

I am getting the error accompanied by an Unexpected log failure

Can anyone please help me>

11,186 Points
2014-08-01 9:15 am
Could you provide us with the exact error that you are getting?
n/a Points
2014-08-27 2:26 am


I am getting an error when I am trying to send emails to some domains(,

This is the mail system at host


I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.


For further assistance, please send mail to postmaster.


If you do so, please include this problem report. You can delete your own text from the attached returned message.


                   The mail system


<>: host[] refused to

    talk to me: 421 Downstream server error


The error I am getting is in bold above. Please explain me the reason and a solution for this.


Thank you very much.

11,186 Points
2014-08-27 11:16 am
It appears that the remote mail server that you are sending to is closing the connection. Unfortunately, as their mail server is outside of our network, we do not have the specific reasoning as to why. For this, I recommend speaking with the individual that you are attempting to send to by other means to identify what on their server may be causing the issue.
n/a Points
2014-08-27 10:41 pm

Hi JrffMa,

Thanks, sure...will try to do that...

n/a Points
2014-10-22 1:25 pm

Been getting this for the last week on mulitple accounts here. When you first attempt to send an email to a wide varity of servers this message will pop up every time. Most times you can just click send again a second later and it will go through but sometimes it will lock you out for almost a full minute. Any idea what caused this and/or how to fix it.

SMTP Error (421): Connection to server failed.

26,266 Points
2014-10-22 1:46 pm
Hello Jason,

Sorry to hear you're having problems with the server connection when you're trying send an email. We need a little more information though. When I checked the server, I found no error messages or problems with connection. I also checked on the server history, and it appear to be okay. There are a large variety of possible factors for this kind of problem, so we need more info in order to help pinpoint the problem. Are you using a computer or device to connect to email? And what specific settings are you using? Do you get any bounceback messages? I'm seeing no error messages in the logs on this end.

Also, please reference Problem with sending email for further help in troubleshooting the issue.

If you can please provide us more information, then we can get back to you after investigating the issue in more depth..

Kindest regards,
Arnel C.
n/a Points
2014-10-22 2:05 pm

I use multiple devices and have been using the same mail settings for years. I use an Imac at the office and an HP laptop in the field. Also, my CFO and receivables manager are having the same problems. I havent noticed issues send from my phone or tablets only desktops and laptops.

As far as bounceback, I havent received any as of yet, but like I said, it usually goes through a second later.

"And what specific settings are you using?" I dont know what you mean specifically, but nothing has changed in the passed week except the errors.

Ill look through the reference guide as well. Its just weird that after not having anything like this ever, then have it happening to multiple people on different accounts, on different computers.


26,266 Points
2014-10-22 2:15 pm
Hello Jason,

I can understand the concern and the confusion on the issue. The problem here is that your device/computer is trying to make the connection to the server. When it does this, anything that causes a delay or interruption in that attempt to deliver could be causing the error. Since we do not have control of your network (only the servers), it's difficult for us to determine what factor could be affecting only the computers of your system. It could be an internal network issue, an ISP (internet service provider) issue, or maybe you are making a connection, but it is slow to synchronize causing a timeout. The settings I'm referring to are the outbound email client settings that you are using to connect to the server. So, if it's a computer, does the problem happen consistently from specific accounts? That information would be invaluable for testing on our end, so that we can determine if the problem does exist on the email server.

We appreciate your patience as we work toward resolving this issue.

Arnel C.
n/a Points
2014-10-22 3:10 pm

It happens with every email I send. Every person that accesses their email via a computer or laptop, has this issue. (in our company that is). As far as timing out, the instant I click send, the error pops up, literally 1 second later I can hit send again and it goes through. As far as the outgoing client settings, no one has made any chages to anything nor would anyone attempt to do so. Additionally, I use my laptop on the road using a wireless connection complete separate and different than any connection at the office and I still have the same issue. It is also a different OS than the computers at work. It seems the only common denominator, is the mail server.

The problem on a whole isnt that serious, but it does sometimes slowly send the email after the error. Sometimes taking over a minute to send a plain text email.

26,266 Points
2014-10-22 4:10 pm
Hello Jason,

Okay, if you're getting the problem across the board with everything connecting to the account, then it's definitely an issue with the mail server. I was able to test here and duplicate the error as well. One thing that may have been causing it is the list maintained for handling remote and local domains for email. Yours is set to local domain - meaning that email is handled by our server. The suggestion given to me by one of our senior techs was to remove your domain temporarily (very briefly), and then re-add it. When I did this, I logged off of my webmail test account, then attempted to re-duplicate the error by logging in and re-sending a test email. The error did not reappear at this point.

Try testing it on your end now. Please let us know if you continue to see any errors. Hopefully, this issue has been resolved.

Kindest regards,
Arnel C.
n/a Points
2014-10-24 7:00 pm

Looks like some changes happened since the last time we talked. There are some new features and yes, there error issue is gone. Thanks for the help.

n/a Points
2015-03-03 10:06 am

We just received notice that people are getting the bounce back with this: 

Failed to connect to Server temporarily not accepting mail at Greeting - 421 4.3.2 Service not available, closing transmission channelServer refused mail at MAIL FROM - 530 5.7.1 Client was not authenticated

I have never seen this before so not sure where to look for the problem. Any help or guideance would be appreciated. Thanks.

5,302 Points
2015-03-03 11:58 am
Hello Jeremy,

This error is stating that the client was not authenticated, this means that you need to make sure you are passing your email accounts password for outgoing mail authentication. Depending on the client you are using it can be done in a few different areas.

Best Regards,
TJ Edens
n/a Points
2015-03-27 1:30 pm

Inmotionhosting (IMH) is hosting our mail server.  We are getting occasional AOL soft bounces, as

Delay reason: SMTP error from remote mail server after end of data: host []: 421 4.2.1 (DYN:T1)

which AOL claims is due to

  • The IP address you are sending from has been temporarily rate limited due to lack of whitelisting, unexpected changes in volume, or poor IP reputation.

My questions:

1. Since AOL is bouncing based on our IP address, is this a function of IMH's server's IP, or our specific account? I would think the former.

2. If the former, then what might IMH do to alleviate this problem?

3. If the latter, what might we have done to cause this, and how might we alleviate it?  To the best of my knowledge, we do not email in bulk.

4. Additionally, occasional emails from AOL to us go missing, but I have not yet traced that problem.

Thank you.

Greg F.

29,167 Points
2015-03-27 4:23 pm
Hello Greg,

I will try to answer you questions as best I can:

1. Since AOL is bouncing based on our IP address, is this a function of IMH's server's IP, or our specific account? I would think the former.
- It is likely the former, particularly if you are on a shared server. If you are on a VPS or Dedicated, then it would be both.

2. If the former, then what might IMH do to alleviate this problem?
- You can email the bounces to our Live Support department and they will check out the situation. If they can repeat it from the server, then it would go to our Systems team to be handled.

3. If the latter, what might we have done to cause this, and how might we alleviate it? To the best of my knowledge, we do not email in bulk.
- If it is the latter, it would have to do with their own set of rules, but we would not have any way to identify them. You would need to reach out to AOL and ask them which rules your emails are violating. But again, the odds are with the server IP being the issue.

4. Additionally, occasional emails from AOL to us go missing, but I have not yet traced that problem.
- If you have incomgin emails missing, you can contact our Live Support and provide the email address and approximate time the email was sent to you. They can then check the server logs to see if any contact was made from AOL side and if so, see how our server dealt with the email.

Kindest Regards,
Scott M
n/a Points
2015-03-31 4:45 am


I'm getting following error message:

"Delay reason: SMTP error from remote mail server after end of data:


    421 Read data from client error"


What does it means?


5,302 Points
2015-03-31 10:55 am
Hello Shuvro,

This can be caused for many reasons. Does this happen every time you try to send an email? Does this happen on many recipients or just certain ones?

Best Regards,
TJ Edens
n/a Points
2015-07-31 12:03 pm



I wonder if you can help.  I get the following error message to only one address (although it occurs with the different names in the address ie and  But it does not happen consistenlty - every now and then one gets through.


Any ideas? does not like recipient.

Remote host said: 421 Service Temporarily Unavailable

Giving up on


I'm not going to try again; this message has been in the queue too long.

5,302 Points
2015-08-01 12:58 pm
Hello Sue,

Can you post the full email header (while modifying the email address) so we may try to help you figure out the issue at hand.

Best Regards,
TJ Edens
n/a Points
2015-08-02 7:30 am

Hi thanks for the offer of help.  This is the main part of the error message.  After this there is a string of information about the return path and thread index as well.  Do you need to see this (with addresses removed).  Sue Hi. This is the qmail-send program at I'm afraid I wasn't able to deliver your message to the following addresses. This is a permanent error; I've given up. Sorry it didn't work out. <>: does not like recipient. Remote host said: 421 Service Temporarily Unavailable Giving up on I'm not going to try again; this message has been in the queue too long. --- Below this line is a copy of the message.

17,917 Points
2015-08-03 10:50 am
Hello Sue,

Thank you for contacting us. This email is being delivered, but the recipient server is denying it due to the following reason:
421 Service Temporarily Unavailable Giving up on

It is a possible spam rule, or blacklisting that is denying the email. Unfortunately, the recipient will have to whitelist you, or review their mail logs for more information.

Thank you,

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