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Common causes of bounced emails

Here are some common causes of bounced emails:

Error	Possible cause	Resolution
Mailbox not found Invalid mailbox User unknown Mailbox unavailable	Wrong email address entered or a problem with the recipient's email account.	Check that you have the correct email address. Wait a while and try again. If the message still bounces, the person may have closed that email account, or they are no longer at McGill.
Mailbox full Quota exceeded	Your contact has too many emails and needs to make some space before they can receive yours.  Can also be a sign of an abandoned account, where your contact may have stopped checking their account and caused their email account to fill up.	Wait for your contact to empty their email account, or try and contact them through another method.
Host unknown Domain look up failed	This means that the example.com part of the email address does not exist; either through a misspelling or the ISP changing its name. For example, attbi.com changed its name to comcast.com, causing any emails sent to attbi.com addresses to be bounced back.	Check that the email address you are sending to is up to date, and accurate.

 

"Unable to relay" errors

This is a blanket term for a host of possible errors, such as:

Error type	Possible cause	Resolution
The "From" address might not match an account on the email server	The ISP might require that email comes via a connection (cable or DSL) actually provided by the ISP - sending using someone else's connection might not be allowed.	The ISP might require you to authenticate before sending email and you haven't.
No adequate servers Connection timed out Resources temporarily unavailable Out of memory	These typically relate to a problem with a mail server, over which you probably don't have any control.	They are, in general, temporary, and should resolve themselves over time. Look carefully at the bounce message; the email server involved may continue to automatically try to deliver your email without any action required on your part.
Blacklist filters	If you see messages that indicate your email was "blocked", or "listed in", and references to sites that have things like "spamcop", "dynablock", "blackhole", "spamhaus" and similar in their names, then your email was probably intentionally blocked because the receiving system thinks your ISP's mail server is a source of spam	Get in touch with your ISP and explain that their server may be on a blacklist somewhere, and then try to use a different email address, or a different email account of your own, to contact your intended recipient. You might also tell your recipient that their ISP is improperly blocking legitimate email
Content filters	Your email looks too much like a spam message and has been blocked by the content filters.	Scan the bounce for any clues (sometimes there's more information), and then validate your recipient can get any email by sending a simpler message. Assuming that all works, then re-work your message as best you can to not look like spam.

 

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Suspicious bounce messages

Have you received "bounced" (email cannot be delivered) warning messages regarding email you never sent?

Do not panic. This may be the result of a spammer or virus forging your email address, but it does not mean your email account has been compromised.  

Spammers and viruses use harvested email addresses in the From field in order to make it appear as if the email comes from someone else (you). When an email cannot be delivered, a warning message is sent to the sender, notifying them that their email bounced. In this case, because the sender address is spoofed/forged, your email address appears to be the sender, so you are receiving the bounced email warnings even though the original message was sent by someone else.

Unfortunately there is nothing that you can do but delete these warning emails and wait it out.

If you have any questions or concerns, please contact the IT Service Desk at 514-398-3398.