Email newsletters - What causes a "failure?"

[farmboy]

Other than the recipient has a full inbox, what causes a failure when attempting to deliver an email message to a subscriber?

FarmBoy

[Receptional Andy]

A few common reasons are:

• Spam filtering: many systems now bounce back messages that set off enough spam triggers
  
• Email account closed, for instances when an employee leaves a company, or an account is inactive for a protracted period of time
  
• Incorrect email address when signing up
  
• The recipients email server couldn't be contacted within a reasonable amount of time
  
• The recipients email server rejects the message for a technical reason (e.g. out of disk space)
  

Most bounces include an error code, which you can use to isolate particular causes.

The gory details of the standard error messages are in the various SMTP RFCs like rfc2821, although I'm sure there's a more accessible summary somewhere online.

[edited by: Receptional_Andy at 8:55 pm (utc) on May 21, 2008]