sendmail, 4th Edition

SoftBounce

Bounce with temporary, not permanent, errors V8.14 and later

Normally, sendmail permanently rejects email using a 5yz SMTP reply code:

RCPT To:<[e-mail]>
553 5.3.0 <[e-mail]>... Spam blocked see: http://spamcop.net/bl.shtml?76.23
.25.147

But because mail rejected with a 5yz code will not be retried, such rejections may not be desirable when testing a new setup. Consider the need to create a new rule set that rejects certain Subject: headers, or the need to develop and install a new Milter. Until such a new setup is validated as working, you might want to fail mail only temporarily instead of permanently.

Email is temporarily failed with a 4yz code and delivery will be retried at a later time (unless the mail is spam).

For testing, you can change all 5yz bounces into 4yz bounces using the SoftBounce option:

O SoftBounce=bool                    ← configuration file (V8.14 and later)
-OSoftBounce=bool                    ← command line (V8.14 and later)
define(`confSOFT_BOUNCE',`bool')     ← mc configuration (V8.14.1 and later)

The argument bool is of type Boolean. If it is missing, the default value is true (deliver single-threaded). If the entire SoftBounce option is missing, the default becomes false (deliver in parallel). The default for the mc configuration technique is false.

With the SoftBounce option set to true, all SMTP replies that would normally begin with a 5 will have that 5 converted into a 4 just before the reply is issued. Note that only the leading 5 is changed, not the entire SMTP value. ...