How to prevent greylisting?

Hi Armand5,

Greylisting is one of the new ways of combating spam.  Basically, each time a mailbox receives an email from an unknown contact, the mail is rejected with a "try again later" message.  This message happens at the server level, and causes the sender's email system to reattempt delivery of the message at a later time.  So, for normally configured email systems, it will result in the recipient getting your message whenever your mail server retries again (typically within 4 hours).  Once the recipients server receives the re-tried message, it will deliver it immediately (and usually will white-list your address going forward).

Did this issue happen to a specific mail provider? If so, please try testing from another few Office 365 mailboxes and see if you get the same problem there. If yes, it probably means the problem wasn't with Exchange, but with the receiving server. Their greylisting does not appear to work.

In most implementations the recipients server will white-list your address once you successfully send a message to the recipient the first time. If this is not the case (i.e. you are consistently getting these bounces back), you may want to check with the recipient and have them check their configuration settings on their server for their greylist.

Thanks,
Mouran