temperamental Mail won't send email
At times when I simply try to reply an email that I have received, Mail gives an error saying that I should select another server. If however I click "edit message" and I copy the content of the email, I close that email (meaning deleting it) and then click reply again on the original email and paste everything in, 90% of the times Mail will simply go ahead and send it. Why? Sometimes I just have to save the email into drafts, send a test email to myself followed by the trying to send the drafts email and it's sent. I don't get it. Is there a bug in Mail or is it my email service provider and how do I find out this problem? I already contacted them and they went like "yeah, you can't write Ltd in your description. Duh?? It has been always like this for years.. I can tell it's not the ISP because at home I have a different ISP and I have the same problem. I also have the same problem both on my iMac and my MacBookPro. All emails are set up in an IMAP configuration so they are in sync with each other. What do you think? Mail problem? Mail setting? Server problem (bluehost) ? ISP problem (WharfT&T or iCable in HK)?
Thank you.
iMac, Mac OS X (10.5.8)