Technical Tip: Error: 'reject=451 4.3.2 Please try again later' from FortiMail

[pchee]

Description	This article describes what to check when receiving the error 'reject=451 4.3.2 Please try again later' from FortiMail.
Scope	FortiMail.
Solution	Sender receive bounce email with a statement: Remote Server returned '<[x.x.x.x] #5.0.0 smtp; 5.x.1 - Maximum number of delivery attempts exceeded. [Default] 451-'4.3.2 Please try again later' (delivery attempts: 3)>' Check on the dedicated cross-search log and notice: Milter: to=<test.account@domain.com>, reject=451 4.3.2 Please try again later  Navigate under Domain & User -> Domain -> Domain FQDN:  Under the LDAP Option -> User alias/address mapping profile, notice that the email address has been cross-mapped to an LDAP profile. Make sure that the LDAP profile connection is still valid and accessible or a 451 error will be generated from FortiMail.