Here is my understanding:
Webmail (gmail, etc) uses http for sending/retrieving emails.
Email clients (thunderbird, etc) use SMTP for sending emails, and POP3/IMAP to retrieve emails. (Or, do they use http to send emails too, and only SMTP servers actually use SMTP..?)
Is this correct?
Edit: I guess my question is a little more subtle. I understand that SMTP server (gmail) to SMTP server (yahoo) is SMTP, and thus email is SMTP. But when gmail or thunderbird connect to their respective SMTP servers, is the connection between SMTP server and the webmail/email client using SMTP to send the mail? the reason i ask is if you look at emails in gmail it says the first it got received was with HTTP, and then it can be bounced around gmail servers using SMTP
Best Answer
All e-mail is sent using SMTP. This is covered in the following RFC 821.
POP3 is a retrieval protocol only and covered in RFC 1939.
IMAP is the same and covered in RFC 3501
All web-based mail providers simply provides an interface to the mailboxes but still apply and use the above protocols which are standards, specificed and defined by the RFC documents. Your e-mail is saved on the provider servers and using the example below then sent from one of their servers.
To expand on this. The best way to understand how to send an e-mail is to do it the way it is done mentioned in the RFC. Here is a step-by-step guide on how to send an e-mail using Telnet with SMTP.