What does 550 stand for?
550 stands for "Mailbox Unavailable"
How to abbreviate "Mailbox Unavailable"?
"Mailbox Unavailable" can be abbreviated as 550
What is the meaning of 550 abbreviation?
The meaning of 550 abbreviation is "Mailbox Unavailable"
What does 550 mean?
550 as abbreviation means "Mailbox Unavailable"
