>> The choice of 521 here seems rather unfortunate, and based on an >> error the experimental RFC 1846. Please consider 550 or similar. > >That's part of the problem: None of the existing codes that can be returned in >response to RCPT TO are right for the job. 550 is a mailbox access error, 552 >is a storage allocation error, 553 is an invalid mailbox error, and 555 is a >parameter problem. Out of all these 553 is probably the closest, but it is >still not quite right. I share your opinion that anything that breaks is already broken, but considering how widely used Postfix is, it might well be better engineering to switch to a 553 code. Topic already raised in appsarea. R's, John