Cameo now handles more automated replies to mailshots, including out-of-office messages.


When a mail server bounces an email, it does not send it to the original From or Reply-To email address. Instead, it replies to a different address, called Sender, hidden in the email header. In domestic email, these are often the same. But for bulk email, we can use a unique Sender address that identifies the intended recipient. This means we can attribute a bounce to the right person.

Secondly, most bounce messages follow a standard (called RFC 3464) that includes a machine-readable part, saying why it failed. (While helpful, many email systems send the same error code for everything, mixing up errors like mailbox full, which is usually temporary, and recipient not found, which is usually permanent).

I’ve been monitoring what other kinds of message arrive via this route since Cameo started capturing these. This has now allowed me to make some improvements.

Non-standard bounces

Some email systems don’t follow this machine-readability standard. They just send a plain text message. This would not be a problem, except there are two other kinds of automated, plain text reply also delivered to Sender:

  • out-of-office replies, where the account owner sets their own text, and
  • delayed delivery replies, where some mail software retries failed delivery attempts several times for up to four days, and only then gives up.

Neither of these cases should cause quarantining of email addresses. But other plain text email are true hard bounces.

Therefore, Cameo now does some analysis of the text to try to distinguish these.

Out-of-office replies

Cameo now includes out-of-office replies in the summary of email problems posted to reminder messages each morning (when there are any). This is so that:

  • you get to know if someone may have received your email but is not going to be reading it any time soon; and
  • in case of false negatives, where Cameo has incorrectly identified a bounce as an out-of-office message.

Cameo identifies out-of-office replies by looking for tell-tale phrases in the message. These include things like vacation, away, office, or break. This is not infallible. It can end up with both:

  • false positives (we see an error message as an out-of-office reply) or
  • false negatives (we see an out-of-office reply as an error). These end up in quarantine.

This may need some fine-tuning, but hopefully these will be rare. Seeing them in the feedback report means you can act on them manually if they do happen.

Similarly, messages identified by distinctive wording as “we’ll keep on trying” holding replies are weeded out. I get copies of these in case of false positives, but you should not see them.

We then treat anything else as a true error.