SMTP Connection: Failed/Pending

SMTP failures can occur due to various reasons. If your SMTP fails, Commusoft will notify you in the app. When an email appears as Pending instead of Sent, it indicates an issue with your SMTP setup. The email will remain Pending until SMTP settings are corrected, and Commusoft will attempt periodic resends to the recipient.

SMTP email delivery failures may stem from issues with the recipient's mailbox or your provider. Previously, Commusoft didn't retry sending failed SMTP emails. Now, we retry multiple times over 24 hours. Some failures may be temporary, like errors or server maintenance. By attempting multiple sends, we boost the chance of successful delivery.

If after 24 hours the email isn't received, Commusoft will send it via our mail provider as a backup, ensuring your message reaches the recipient. For technical insight into SMTP issues, refer to the information below. While not directly related to Commusoft, it may aid in understanding SMTP complexities.


Code Meaning How to solve it / What to do
101 The server is unable to connect. Try to change the server's name (maybe it was spelt incorrectly) or the connection port.
111 Connection refused or inability to open an SMTP stream. This error normally refers to a connection issue with the remote SMTP server, depending on firewalls or misspelt domains. Double-check all the configurations and in case ask your provider.
211 System status message or help reply. It comes with more information about the server.
214 A response to the HELP command. It contains information about your particular server, normally pointing to a FAQ page.
220 The server is ready. It's just a welcome message. Just read it and be happy that everything is working
221 The server is closing its transmission channel. It can come with side messages like "Goodbye" or "Closing connection". The mailing session is going to end, which simply means that all messages have been processed.
250 Its typical side message is "Requested mail action okay completed": meaning that the server has transmitted a message. The opposite of an error: everything has worked and your email has been delivered.
251 "User not local will forward": the recipient's account is not on the present server, so it will be relayed to another. It's a normal transfer action. For other information check out our article on what is an SMTP server.
252 The server cannot verify the user, but it will try to deliver the message anyway. The recipient's email account is valid, but not verifiable. Normally the server relays the message to another one that will be able to check it.
354 The side message can be very cryptic ("Start mail input end <CRLF>.<CRLF>"). It's the typical response to the DATA command. The server has received the "From" and "To" details of the email, and is ready to get the body of the message.
420 "Timeout connection problem": there have been issues during the message transfer. This error message is produced only by GroupWise servers. Either your email has been blocked by the recipient's firewall, or there's a hardware problem. Check with your provider.
421 The service is unavailable due to a connection problem: it may refer to an exceeded limit of simultaneous connections, or a more general temporary problem. The server (yours or the recipient's) is not available at the moment, so the dispatch will be tried again later.
422 The recipient's mailbox has exceeded its storage limit. Best is to contact the user via another channel to alert him and ask to create some free room in his mailbox.
431 Not enough space on the disk, or an "out of memory" condition due to a file overload. This error may depend on too many messages sent to a particular domain. You should try again sending smaller sets of emails instead of one big mail-out.
432 Typical side-message: "The recipient's Exchange Server incoming mail queue has been stopped". It's a Microsoft Exchange Server's SMTP error code. You should contact it to get more information: generally, it's due to a connection problem.
441 The recipient's server is not responding. There's an issue with the user's incoming server: yours will try again to contact it.
442 The connection was dropped during the transmission. A typical network connection problem, probably due to your router: check it immediately.
446 The maximum hop count was exceeded for the message: an internal loop has occurred. Ask your SMTP provider to verify what has happened.
447 Your outgoing message timed out because of issues concerning the incoming server. This happens generally when you exceeded your server's limit regarding the number of recipients for a message. Try to send it again segmenting the list in different parts.
449 A routing error. Like error 432, it's related only to Microsoft Exchange. Use WinRoute.
450 "Requested action not taken – The user's mailbox is unavailable". The mailbox has been corrupted or placed on an offline server, or your email hasn't been accepted for IP problems or blacklisting. The server will retry to mail the message again, after some time. Anyway, verify that is working on a reliable IP address.
451 "Requested action aborted – Local error in processing". Your ISP's server or the server that got a first relay from yours has encountered a connection problem. It's normally a transient error due to a message overload, but it can refer also to rejection due to a remote antispam filter. If it keeps repeating, ask your SMTP provider to check the situation. (If you're sending a large bulk email with a free one that can be a common issue).
452 Too many emails sent or too many recipients: more in general, a server storage limit exceeded. Again, the typical cause is a message overload. Usually, the next try will succeed: in case of problems on your server it will come with a side-message like "Out of memory".
471 An error of your mail server, often due to an issue of the local anti-spam filter. Contact your SMTP service provider to fix the situation.
500 A syntax error: the server couldn't recognize the command. It may be caused by a bad interaction of the server with your firewall or antivirus. Read carefully their instructions to solve it.
501 Another syntax error, not in the command but in its parameters or arguments. In the majority of cases, it's due to an invalid email address, but it can also be associated with connection problems (and again, an issue concerning your antivirus settings).
502 The command is not implemented. The command has not been activated yet on your own server. Contact your provider to know more about it.
503 The server has encountered a bad sequence of commands, or it requires an authentication. In case of "bad sequence", the server has pulled off its commands in a wrong order, usually because of a broken connection. If an authentication is needed, you should enter your username and password.
504 A command parameter is not implemented. Like error 501, is a syntax problem; you should ask your provider.
510/511 Bad email address. One of the addresses in your TO, CC or BBC line doesn't exist. Check again your recipients' accounts and correct any possible misspelling.
512 A DNS error: the host server for the recipient's domain name cannot be found. Check again all your recipients' addresses: there will likely be an error in a domain name (like mail@domain.coom instead of
513 "Address type is incorrect": another problem concerning address misspelling. In a few cases, however, it's related to an authentication issue. Doublecheck your recipients' addresses and correct any mistake. If everything's ok and the error persists, then it's caused by a configuration issue (simply, the server needs an authentication).
523 The total size of your mailing exceeds the recipient server's limits. Re-send your message splitting the list in smaller subsets.
530 Normally, an authentication problem. But sometimes it's about the recipient's server blacklisting yours, or an invalid email address. Configure your settings providing a username+password authentication. If the error persists, check all your recipients' addresses and if you've been blacklisted.
541 The recipient address rejected your message: normally, it's an error caused by an anti-spam filter. Your message has been detected and labelled as spam. You must ask the recipient to whitelist you.
550 It usually defines a non-existent email address on the remote side. Though it can be returned also by the recipient's firewall (or when the incoming server is down), the great majority of errors 550 simply tell that the recipient email address doesn't exist. You should contact the recipient otherwise and get the right address.
551 "User not local or invalid address – Relay denied". Meaning, if both your address and the recipient's are not locally hosted by the server, a relay can be interrupted. It's a (not very clever) strategy to prevent spamming. You should contact your ISP and ask them to allow you as a certified sender. Of course, with a professional SMTP provider like turboSMTP, you won't ever deal with this issue
552 "Requested mail actions aborted – Exceeded storage allocation": simply put, the recipient's mailbox has exceeded its limits. Try to send a lighter message: that usually happens when you dispatch emails with big attachments, so check them first.
553 "Requested action not taken – Mailbox name invalid". That is, there's an incorrect email address into the recipient's line. Check all the addresses in the TO, CC and BCC field. There should be an error or a misspelling somewhere.
554 This means that the transaction has failed. It's a permanent error and the server will not try to send the message again. The incoming server thinks that your email is spam, or your IP has been blacklisted. Check carefully if you ended up in some spam lists, or rely on a professional SMTP service like turboSMTP that will nullify this problem