e-mail stuff, I read the article and now I have more questions
So "MUA" ("Message User Agent") is just a weird word for "e-mail client"? Some things make a lot more sense now!
Your e-mail client sends the message to the mail server (MTA) where you [the sender] have an account (how? which protocol does that part of the connection use?), and the mail server then establishes a connection to the receiver's mail server and sends it the message over SMTP. It finds the receiver's mail server by looking up the MX record for the receiver's domain? Did I understand that correctly?
That article by Cloudflare also implies that there might be multiple hops, rather than the sender's mail server connecting directly to the receiver's mail server? When does that happen?
And then the Mail Delivery Agent (MDA) just handles IMAP with the receiver's e-mail client? It does not communicate with other mail servers?
re: e-mail stuff, I read the article and now I have more questions
Your e-mail client sends the message to the mail server (MTA) where you [the sender] have an account (how? which protocol does that part of the connection use?)
this is SMTP. you connect to a mail server, send it some mail to relay, and then it will relay that mail. strictly, this does not require authentication, but nobody allows that anymore these days because the spam potential is enormous otherwise
It finds the receiver's mail server by looking up the MX record for the receiver's domain?
yes. setting up DNS is more much complicated fur Many Reasons, however
That article by Cloudflare also implies that there might be multiple hops, rather than the sender's mail server connecting directly to the receiver's mail server? When does that happen?
very large mail service purroviders might have complex MTA networks passing mail along multiple servers. fur whatever reason. i’m really not sure why, besides load balancing. if you inspect the headers fur a lot of emails you receive, there will often be a papurr trail left behind detailing some of the shenanigans
And then the Mail Delivery Agent (MDA) just handles IMAP with the receiver's e-mail client?
this is still SMTP. the MDA takes mails that are identified as being handled locally and places them in the relevant mailbox. if you set up a basic mail server on your machine, it will purrobably be set up by default to include an MDA fur sending mail to on-machine users
re: e-mail stuff, I read the article and now I have more questions
@vaporeon_ (remote) email delivery is an act of server-to-server commewnication, in more or less the same way AP works. the client authenticates with their server to author a message as threatened themself; the actual mail delivery is defurred to the MTA you requested send an email on your behalf. (without requiring authentication, SMTP makes no guarantees that anybody authoring a message is actually the purrson they are claiming to be, and you could send infinite emails as any arbitrary purrson)
theoretically, you could effectively impurrsonate an MTA and purrform a server to server exchange to send mail to a recipient, which is another vector fur spam; the ways to deal with this are, unfurtunately, quite layered lol
re: e-mail stuff, I read the article and now I have more questions
@aescling
So from a technical perspective, nothing would stop me from directly establishing an SMTP connection with the receiver's mail server and sending them the message? No need for me to have an account on a mail server, only for the receiver? But in practice, you can't do that, because otherwise that would be used to send lots of spam, so they require authentication? (Where does the authentication happen? Is that part of the SMTP protocol?)