mail can not send from client mail on PC

[kilburn]

There's no "bulletproof" methodology to ensure your mails are not marked as spam in gmail/yahoo/whatever. Obviously, if such thing was possible, every spammer out there would use this method and everyone would end up covered by spam.

That said, make sure that:
1) Your domain's spf records are set and correct
2) Your mailserver uses an appropiate helo
3) Your server is not listed in any blacklist

I'll send you my mail through pm, so you can send me a message and I'll see if there's something misconfigured...