VirtualNames

This occurs when mail is sent to a recipient with badly configured mail filtering systems, and is mostly seen when using webmail. This bounce message occurs when the receiving mailserver has a front-end filter installed which tells us it supports 8 bit MIME characters and accepts our message, but then cannot deliver the message to the backend server because that does not support 8 bit MIME.

If the recipients frontend server didn't advertise that it supports 8 bit MIME, we would automatically convert the message and send it 7 bit MIME, which it could support. Usually the receiving system is using Microsoft Exchange Server and Microsoft are aware of this problem and have a KnowledgeBase article on how this can be fixed here: http://support.microsoft.com/default.aspx?scid=kb;en-us;Q262168

Common questions

Can't you fix this your end?

As this isn't a problem with our servers and is caused by badly configured servers at the receiving end, we can't easily fix it at our end.

Can't you force webmail to only use 7 bit MIME?

In theory this might be possible, but why should we? We use a standards compliant webmail system and forcing it to use 7 bit MIME would make it non-standard and needlessly increase the size of messages sent to servers that are configured properly.