Currently using latest SM 15.x entp build.
Have one specific domain user when sending email to recipient hosted on other server then email is rejected with error message as below
Failed Recipient: recipient_email_id
Reason: Remote host said: 450 4.1.7 <email@example.com>: Sender address
rejected: unverified address: host mail.bb.com[xxx.xxx.xxx.xxx] said: 451
Greylisted, please try again in 60 seconds (in reply to RCPT TO command)
Above us happening repeatedly even after 60 seconds retry's, though i have asked recipient team to whitelist customer email id/ip address but how above can be resolved
NOTE: only this domain user's is facing this issue and rest other domains no such issues.