aquabob,

When you send from your Outlook client it may be trying to relay off a different authoritative mail server. This could cause your mail to end up in their spam folder since you are sending from an autoritatve mail server that is not your own.

Setting up and SPF Record should resolve the trouble you are experiencing. You may want to get in contact with whoever hosts your email and domain in regards to setting up an SPF Record.

Hope this helps.

Mophead