Can't send emails

Hi.

I can receive emails but keep getting a "Cannot send message using the server ___" error message when trying to send emails through two different accounts when using Mail. The first account is through Hostway and the second is through Mac. I believe both accounts are currently working fine as I've sent test emails through their web interfaces.

Also, using both through Mail was working working just fine over the past days, even when using my computer in a hotel on their wireless connection. Now that I'm back home where it always works, I can't seem to send anything out.

I've tried rebooting the computer and my modem and wireless router. I've changed the port from 25 to 587. I've tried changing the authentication to a password. Nothing seems to be working. I'm now awaiting word back from Hostway but since I also cannot send via my Mac account I'm assuming this is a problem with Mail.

Any insights would be much appreciated!