@user_4spwht Thanks for bringing your email concerns to our attention. I cam understand how frustrating this can be. This can happen from a few things such as incorrect SMTP server settings, firewalls or antivirus software blocking access, scheduled message settings etc.

Lets work together to figure this out and provide you with a resolution.

What browser are you using? Have you tried using a different one?

When did this start?

Is it all messages or just some?

Do you have any additional email clients set up such as Outlook, iMail etc?

I have the exact same problem. The weird thing is it comes and goes. Never had the problem until a few weeks ago. Drove me crazy - Comcast was no help at all. Then it went away. Came back today. On all three computers:I have two at work and one at home. All desktop. I have read the history on this problem - been around for at least three years. What the heck? 

Despite all the claims of wanting to help, and "expertise," it's obvious from this thread and others like it that Comcast has decided that analyzing and fixing this issue isn't worth resource expenditure.

One solution, as XfinityBenjaminM said, is using a 3rd-party email client.  In fact the only reason I'm using buggy Xfinity webmail is because I've temporarily lost access to Outlook (I have a paid desktop version).

But another solution is to simply compose the email in an external app like Microsoft Word, Notepad, or a similar Mac or iPad utility, and copy it to the clipboard.  Then open the Xfinity Webmail compose template, ensure it's addressed properly, and paste in what you wrote.  You might even have time to do a little tweaking of the message before the unpredictable trigger-finger Xfinity Mail sends it to Drafts (or worse yet, attempts to save a draft but then says the draft's been deleted from the server.) Then Send.