CiviCRM Community Forums (archive)

I spent some time debugging a fatal error generated when Civimail attempted to send out a test mailing: "Recipient is not recognized".

I traced this back to a Return-Path header that looked, for instance, like this:
"b.11.8.517ddbf66b9c405b@"

I had a reasonable setting for the bounce handling email account under Administer->CiviMail->Mail Accounts, but had neglected to set the default checkbox.

Once I checked []Default, all was well.