Bounce

Common bounce errors

550 sender has failed strict spf –

The sender/FROM domain fails strict SPF checking. The FROM domain does not pass spf.

550 This message was classified as rSPAM and may not be delivered –

The message has been marked as spam and not delivered.

550 This message has a blank subject –

The message was sent with out a subject.

550 err commondomain This message from domain does not pass SPF checks –

The FROM domain is a common domain and does not pass SPF checks. Common causes are a FROM domain of a common mail provider like @gmail

550 recipient domain does not resolve to any MX –

The recipient domain does not resolve to any Mail server.