OS X Mail will not send replies

Hello, maybe someone can help with this. I can create and send a new message in Mail fine. But when I reply to an e-mail message from someone else it just sits in my Outboox. Eventually an "Error" message pops up:

"This message could not be delivered and will remain in your Outbox until it can be delivered. Sending the message content to the server failed."

My only option is to "Close Window"

I know the person's e-mail address is legit. I can send them a new message, just can't reply. Seems to be that way on any attempt to reply.

Appreciate any help.

I'm taking a stab in the dark here, but try this:

In Mail go MAIL > PREFERENCES > (select the account you are trying to send from) > COMPOSING > RESPONDING > Uncheck the box: "Use the same message format as the original message".

...and give it a try. There are some other settings there too that you can play with.

Like I said, just a stab in the dark.

Hi baggss, thanks. It looked like it was unchecked, tried checking it as well as changing other settings there. Noticed that it has trouble forwrding as well. Only "new" messages go through w/o a hitch.

Do you have more than one account? Is the 'from' in your replies look right?

I suppose this could be an issue with your ISP as well. Have you tried it with another computer and the same account?

Hi again, there is just the one account.

Apple help line thought it might be the ISP. However, I hooked my old PC back up (Outlook Express) and everything worked fine. I talked to my ISP (Verizon), they said they only support Outlook or Outlook Express, that's pretty weak as at time of signup their literature said they support Macs.

I like the way Mac Mail integrates with everything else. Would Mozilla Thunderbird, or some other mail app, work as well and maybe fix this issue?

Hey, I was poking around on the Internet some more. It looks like many have had Mac Mail troubles with Verizon. The following seems to have fixed the issue (so far).

http://expertmacintoshconsulting.com/cgi-bin/helpdesk/kb.cgi?action=read;id=34;lang=en

Go to: Apple Menu > System Preferences > Network > Built-In Ethernet > Ethernet TAB > Configure/Manually > Max Packet Size(MTU)/Custon > set to '1492' > Apply

Wish I could rename the thread to "Mac Mail & Verizon DSL" or something. I imagine many people in Verizon's area run into this issue.

Thanks again for the help guys, be seeing you around Mac Forums!