This article explains some of the common responses and will hopefully understand you help why your message bounced and what you can do about it.
The first thing to note is do not be frightened by these emails, although they look technical theya re quite easy to understand adn even more so with this guide. If you read down them there will be all the infromation you need somewhere. For example:
This message has been rejected because it hasThe above, when you find the message at the bottom of the NDR, actually says what's happended. You have forwarded an email, as an attachement, using Microsoft Outlook, or similar, and this has attached the original email as a .eml file. Unfortunately .eml files are unsafe as they can carry and execute viruses so our server like most others, has refused this message. Either ZIP up the message and then forward it or just forward the message normally; not as an attachment.
potentially executable content
This form of attachment has been used by
recent viruses or other malware.
If you meant to send this file then please
package it up as a zip file and resend it
Another common NDR message is something like:
Reason 550: SPF 111.222.333.444 is not allowed to send mail for yourdomain.comBasically the sender of the email has something called an SPF record set up for their domain which is a mechanism that states what mail servers they allow to send emails on behalf of their domain. This is great, it's a good anti-spam method. When they send a message to our servers they see the SPF record and check the message is from one of those defined mail servers; if it isn't it quite rightly refuses it with a message such as the above.
So if you have sent a message and had it bounced for the above reason then you need to contact your email host and ask them to ensure your SPF records include the mail server you are sending via. If in doubt contact you host and send them this link so they know what you mean.