Mozilla Thunderbird

Alright, look... I could really use some help with this...

Basically, I’m entering everything perfectly—username, password, the whole nine yards—but I keep getting hit with this error: Thunderbird can't find the settings for your email account.

I know I have to manually configure the incoming and outgoing servers, POP3, SSL, the standard password stuff... but honestly, I've completely lost my mind trying to get this right.

Here’s how I set mine up (using Comcast):
Honestly, the easiest way is just to create a brand-new mail account and let the setup wizard do the heavy lifting. You just step in and tweak whatever the automation gets wrong.
First, right-click in the left panel, hit Settings, and once you’re in Account Settings, look for Account Actions at the bottom.

Add mail account

Your Name: whatever you want
Email address: Your email here
Password: Use your current one
Check the box for Remember pass
Next>
Pick the POP3 server (assuming that's what your provider uses)

Scroll down to Manual config to open up the detailed settings:
Incoming:
POP3
pop.comcast.net (this is from the provider)
Port: 110
SSL : STARTTLS
Normal password

Outgoing Server (SMTP):
Server Name: mail.comcast.net
Port: 25
Connection Security: STARTTLS
Authentication method: Normal password
At the bottom, make sure to fix the User name (since Thunder tends to add an extra suffix to the address)
User Name:

I think later on you can just right-click the email address and fix things individually under each server—though I’m mostly speaking from memory, except for the password part.

This guide is specifically for an American provider using a POP server. If you're using IMAP, you still need to stick to your specific provider's SMTP server and its details, otherwise, your emails won't actually send...