You might get the following error when sending out mails to an e-mail address which you _know_ is valid: Permanent Failure – Probe failed: Illegal To: address (invalid domain name). While the error message itself is pretty self-explanatory, it’s something that can easily be overlooked – the domain name of your recipient is miss-spelled.
Take the following e-mail address for example:
**To: “Firstname Lastname” <name@domain.com > **
At first sight, that looks pretty valid. However, there’s an added space at the end (right before the ‘>’-sign), that will cause the domain name to be considered invalid. Most e-mail clients would strip excess spaces at the beginning or end, but not all of them. Double check your domain name for the person you’re sending mail to, and keep an eye on the little details.