There is no way for you to adjust line spacing in Comcast webmail. It sounds like the recipient's email service or program in rendering the formatting differently. I'm curious, what domain is the recipient using? Yahoo, Outlook.com, Gmail, something else?
I finally found a solution based on another user's response to a different question. Instead of hitting the return key to get to the next line, you have to hit shift/return. An extra space between the lines will not be added. If you want one space between paragraphs, then you would hit shift/return twice.
The shift-return option proposed above works - but since there's no evidence on the screen that you actually hit the shift key this doesn't seem to be a good solution to me - you won't be able to predict what the recipient will see with any certainty. I like spacing between paragraphs, and the only solution I can see that has no risk of screw-up is to compose an email without spaces and let the system enter them for you. If you dn't like spaces between paragraphs you'll have to use the shift-return. Grade F beta testing. FYI, I just spent far too long on the comcast prolonged-pain-no-help line and the nice gal on their end told me she couldn't even replicate the problem - said it looked great to her from one end to the other - and if that's true there's little hope of ever solving this bone-headed problem. (That was a second-level person, unbelievably the first-level wasn't even capable of sending an email to herself to test it.)
Funny, I got to this thread because I was finally irritated enough to try to find out the solution to this pesky problem. I use mac OS and Safari and although I haven't tried I wonder if it's a function of the browser? Anyway, I sent myself mail to another account where I use Outlook on Windows and sure enough there are two lines per paragraph. Again, really irritating.
Thanks for the Shift-Return trick.
I am so frustrated with Xfinity / Comcast web mail.
There are so many annoying nuances that I am ready to set my forwarding instructions and go gmail.
I spoke with Comcast second level support about this problem. She was very attentive and really wanted to help, but this remains an open issue, which we duplicated while on the phone in Safari, Firefox, and Chrome.
I have another issues where "cut & pastes" into the compse window of Comcast webmail usually causes "blank" characters to be deleted at the end of the sentences (so sentences run together with only a period separating them). That issue, appears to be specific to Safari -- did not happen on Firefox or Chrome.
This really is a pain in the you-know-where. I've never seen any email client -- or any desktop-publishing program for that matter -- exhibit this behavior. It's totally non-standard. Just goes to show that the Comcast developers are ignorant about usability, or just plain ignorant.
Note that there are multiple threads regarding this problem, which was first reported in January -- nearly six (6) months ago. Plenty of time for them to have fixed it by now. Either it's not a priority for them, or they simply don't care.
The Comcast customer support people do care, at least when you escalate, my rep spent about an hour on the phone duplicating the issue. It's just that development does nothing. It's a known issue according to the support rep, but they have no status, no ETA for a fix, nothing. They added me to the "high priority" list to be contacted (by email) when there is an update on this problem, but there have been no updates and at this point I don't expect anything. This problem still continues to kill me because very often subsequent paragraphs in emails aren't read because there is way too much space between paragraphs and it looks like the email has only one paragraph and people often don't see the rest. If I remember, I use Shift-CR to reduce the spaces from something like 5 to something like 3, but it's very easy to forget to do that and even when I do that, it's still often too much space. This bug is costing me business. It may also cost Comcast my business, because email is unusable for me, but they don't seem to care at all.