Video presentation: Computer Networks and the Internet.
2.3 Email. Email infrastructure (mail clients, SMTP servers), SMTP and IMAP protocols.

Computer networks class.
Jim Kurose
Textbook reading: Section 2.3 Computer Networking: a TopDown Approach (8th edition), J.F. Kurose, K.W. Ross, Pearson, 2020.
See http://gaia.cs.umass.edu/kurose_ross for more open student resources.