When an email is received from fred@bloggs.com, our server will lookup the server responsible for accepting email for bloggs.com and attempt to send an email to fred@bloggs.com via that server. We would in all cases expect this to succeed, but when it fails we refuse the email.

This check simply ensures that the sender is a valid mailbox. We do not actually send an email to the sender, we simply check the mailbox exists. This is fairly standard procedure for any good mail router.

If you are receiving this email when trying to send email, then its likely that

• The email you are sending from is incorrect or invalid
• The email you are sending from is temporarily disabled (over quota etc)
• The email you are sending from is malformed

As long as all these are not true, then the issue will be with your email service, which is rejecting your mailbox during the attempt to send to it. You should contact your email provider and have them look into it. To aid their investigation, our email check will appear in their logs as double-bounce@reliance.gen.net.uk, which is of course a valid email address.