Mailbox is full
The most common user problem is a full mailbox. Most systems have a limit on how much email is allow to reside on the server for each user, and once that limit is reached, there is no room to accept new incoming mail. The following are all examples of email error messages caused by a full mailbox:
email@example.com>: User is over the quota. You can try again later.
<firstname.lastname@example.org>: host in7.ibm.net said:
552 <email@example.com>... Mailbox is full
procmail: Mailbox limit exceeded while appending message
550 <firstname.lastname@example.org>... Can't create output
<email@example.com>: host mail9.hotmail.com said:
552 Requested mail action aborted: exceeded storage allocation
This error will stop as soon as the receipient makes additional room in their mailbox (usually by removing old messages from the server), so you should probably resend your message a little later. However, especially with free accounts, this message could actually mean the user no longer checks the account; a good rule of thumb is if you continue to receive this error for more than two weeks, it is likely that the account is no longer in use.