Are u using the mail app on your iMac or Xfinity connect? If u haven't tried the native mail app it's easy to set up. Just open the envelope in your dock and go to mail preferences or system preferences, internet accounts. It varies depending on which Mac OS you're using.
I"m runningh High Sierra on a late 2013 iMAC Version 10.13.6 (I've got a bunch of Word 2011 stuff that's all 32 byte that won't work on new 64 byte tech.) I'm 83 and a real dunce-- so please be gentle (hahaha) I just use the MacMail that comes on the machine- I'm a Florida snowbird, so I get some mail from G mail and Spectrum. Everything seems to come into the MACMail but I can't seem to get anything to send out of the MacMail site-- so I have to go back to Xfinity and it's a real drag. I keep changing passwords because my memory is shot and it never seems to recognize passwords. I don't know where to find the envelope you're speaking of. Could you repeat in baby talk sso I'd understandd. I would truly appreciate this. MB3
Okay, first thing is u can get an Microsoft Office 365 subscription for your iMac for around $60ish for a year. You'll then be 64 bit. I'm using a mid 2012 MacBook Pro with Mac OS Catalina. For your mail assuming your password is changed on your Xfinity account, open up mail from the dock. At the top left next to the Apple, hit mail and choose preferences. Choose accounts, Comcast, under account information check enable this account. On the server settings tab, make sure this is what u have.
incoming server: your email, correct password, host is imap.comcast.net
outgoing server: account Comcast, email address, password,
host is smtp.comcast.net
check in box wherever it says automatically manage connection settings. Restart. Anytime change your Comcast password restart your Mac.
you can also try to enter your email information thru system preferences, but I think your issue is the info for the smtp server. Thru system preferences, internet accounts, click Comcast, enter your first and last name and password. Wait for your iMac to connect to the Comcast server. Good luck. Nothing against Comcast techs but 1-800-275-2273 is Apple care. They'll help with software support and send u support documents. No charge. There may be a wait time as apple stores are currently closed. Good luck.
thank you so much for your prompt reply (all of us sitting here at their computers) I"m printing it out to digest. Agree about Apple Care. They are the most patient sweetest most knowledgeable people in the entire digital world. Every one of them. But they remind me that Comcast is a third party and they can't get into the innards to make this go away. Comcast won't go beyond repeated robots (you used to get Finipinos who just kept saying "I'm sorry" and couldn't do anyhting to fix it.
Are u able to send mail from Xfinity connect? If so it's definitely your Mac mail settings. I would like to recommend Tech Talk America. A website and on You Tube. A teaching site for Mac users by David A Cox. There is an abundance of information there. Good luck.