GMail treats mails from my domain as spam. Why? How to avoid it?

Question

Whenever I send a mail from myaccount@mydomain.com to a gmail account, gmail treats it as spam.

I'm talking about the one e-mail I send to a prospect after I've met him (it is surely non-spam mail). It's happend several times already:

"Hey!, you never sent that e-mail you promised me" the prospect says.

"How come...? I did send it. Check the spam e-mail" I answer.

"Oh, there it is..."

I think it has to do with mydomain.com not being a well-known domain.

How/Where should I complaint about this?

Answer 1

Jeff Atwood had a really good post on things to do to help your email get through. This made a huge difference for the company I work for. Some highlights:

1. Make sure the computer sending the email has a Reverse PTR record.
2. Configure DomainKeys Identified Mail in your DNS and code.
3. Set up a SenderID record in your DNS.

Answer 2

This page might be helpful to you:

https://mail.google.com/support/bin/answer.py?answer=81126

While it applies to bulk-mail messages, there is quite a bit of information about why messages can be marked as spam. I don't know anything about your specific information, but hopefully you'll be able to see something that will be helpful.