Understanding email errors & failures

“Why didn’t my email go through?” The protocol for sending emails is called Simple Mail Transport Protocol (SMTP) and when it fails there could be hundreds of possible reasons why that happened.

Many times when an email was not transmitted successfully you will receive a bounced email that includes one of many numbered SMTP error codes.  These error numbers can be very helpful for diagnosing and correcting problems that prevent successfully sending email.

The bounced message appearing in your inbox usually comes from “This email address is being protected from spambots. You need JavaScript enabled to view it.” and often has a subject line reading “Message Delivery Failure.” The message may say “Delivery to the following recipients failed permanently” and below that may be found the SMTP error message number.

Error number 550-5.1.1 means the email address you entered does not exist. Check your spelling of the name. If the error is 553-5.1.2 the domain name is wrong. Check to be sure you did not misspell gmail.com as geemail.com.

You may see error 421-4.7.0 when an unusually high number of emails originate from your IP address.  Expect to see that one if you are using public Wi-Fi and there are a dozen other patrons at the coffee shop all sending emails.

452-4.2.2 usually means the recipient’s inbox is full and cannot accept any more emails while 552-5.2.2 means the email recipient has gone over a daily limit of how many messages they are permitted to receive in one day.

Error message 452-4.5.3 indicates the email you tried to send has too many recipients.  You can expect to be identified as a spammer when you try sending one email to too many people at once.

535-5.7.1 means your username or password, usually the one saved on your device, was not recognized.  530-5.5.1 usually means the security settings on your computer are not configured correctly.

550-5.4.5 usually means you have sent too many emails today and cannot send any more until you wait a while.  550-5.7.1 means the receiving server tagged your mail as being unsolicited spam and blocked it.

552-5.2.3 means you are trying to send an email attachment that is too big.  Most email servers have a size limit for attachments, and unfortunately the limit is set by company policy and differs from company to company.

And finally (for today), 421-4.4.5 or 450-4.2.1 means nothing is wrong at all except that a mail server is just too busy right now. Try sending your email again later.

As you can see, there could be many different reasons why you email did not go through to its destination.  There are more SMTP error codes than listed here, many many more.  If you received a bounced email you should do a web search of the number to find more information pertaining to that specific error number.

Charles Miller is a freelance computer consultant with more than 20 years IT experience and a Texan with a lifetime love for Mexico.  The opinions expressed are his own.  He may be contacted through his website at SMAguru.com.