Email not sending from iphone

I am using my mail app. Have been using it for years without any issues but now I cannot send any emails. 

Hey there user_t2dbib. I know you mentioned having changed the password and checking the outgoing settings. When the password is changed, with the Mail app you would want to fully delete your Xfinity email from the Mail app and then add it again with the updated password. That should let you send and receive emails again. Let me know if that works? Have you attempted to sign in on the Xfinity website, to see if it uis functioning fully on there?

I've tried this but can't get the account back on my iPhone.  After entering the information, the "verifying" runs for a long time and then says The SMTP server "smtp.comcast.net" is not responding.  Check your network connection and that you entered the correct information in the Outgoing Mail Server" field.  In the add new account field on opening an account, there is no place to enter the smtp info but the veryfying screen shows outgoing mail server info including a password.  I did not have the problem before and had not changed the password between the time I could send emails from the phone and now.  I am using the Mail app on the phone.

Also, on my pc, some sent messages are not showing up as sent on Outlook, while they do show up as sent when I log on to the Xfinity site.

@user_no1oqc I’m sorry to hear you're still having an issue. I would like to take a step back and provide you with a link that has the steps and settings for various email programs including the settings for an iPhone and PCs. https://www.xfinity.com/support/articles/email-client-programs-with-xfinity-email

Can you double-check and ensure all the information you’ve entered is correct and up to date for all your devices and try again. 

Please avoid using any saved previously filled saved passwords or prefill information and enter everything manually.

If you see that password error I would like for you to reset your XFINITY password for your username.

You can follow the steps in this link to create a new password http://www.xfinity.com/password.