I use Gmail for all my email, and most of the domains I own are verified by Google and I can send mail through them (using smtp.google.com). This mostly seems to work, but there are a few people who never get emails I send using one of my alternate accounts.
I've followed all the instructions on Google's Help Pages, and they're weren't helpful: yes, I was sending to the correct address, and the emails show up in Sent Mail, and I don't get bounce notifications, and the recipients don't get my emails in their Spam folders. The emails just don't arrive. Sending an email from one of my other addresses works, which implies to me it's something to do with the specific email address I'm sending from.
How can I figure out what the problem is, and fix it?
Best Answer
Your domain needs a Sender Policy Framework - see SPF record.
Though it is not a standard, it is highly recommended as an anti-SPAM measure.
It is optional but some stupid mail servers reject mail if this record is not present.
Here is Google Support on how to set it.