When an email is received the mail server goes through a series of checks to determine what should happen with the email. The following steps explain what happens if you have more complicated mail setups that involve mailboxes, forwarders and catch-all forwarders.
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[*]If there is a mailbox for the email address then the email will be delivered to the mailbox.
[*]If there is a forwarder for the email address then the email will be forwarded. This happens even if the email has also been delivered to a mailbox.
[*]Only if there is no mailbox and no forwarder for the email address then the mail server looks for a catch-all forwarder. If there is one then the mail is forwarded.
[*]If a forwarder or catch-all forwarder is set to forward the email to a different email address on the same domain name then the checks will be made again. This can result in emails being forwarded in a loop, in which case the email would just be rejected.