Try putting a comma after each address in the spreadsheet entries and then copy them. It works for me that way using Mac Numbers. I would assume it would work the same way in Excel.
I have used that method successfully on Xfinity's previous email platform but Comcast now admits that the new platform will not accept multiple emails pasted on its new email page. I have been told that the techs are "working on it". In the meantime I had to revert to using yahoo, gmail, etc. to send out large group messages. Thanks for taking time to offer your suggestion.
But I'm telling you I can do it. I've copied and pasted multiple email addresses from Mac Numbers, a Mac Pages document, the body of an email etc. Basically, most anywhere you can copy and paste from as long as you put a comma between them. I don't know who told you that you can't, but I'm saying you can. Try it from a Word document or something and see if it works for you.
I have tried all methods that you have suggested without any success. I am now going to assume that there might be a compatabilty issue with PC's. Again, Comcast is aware of this specific issue (without mentioning that it does not apply to Apple programs) Thank you for all your efforts on my behalf.
I am at a loss here to figure out what is going on with your account. I just tried it on my Windows 10 Dell laptop. I typed out three of my other email addresses in Notepad, and three others in Wordpad, separated with commas-------------worked like a charm both times. So I don't think it's anything to do with the operating system on your computer.
Every time I insert multiple emails into the address box I get an error message in xfinity. I have tried separating the addresses with both commas and semi-colons.