(older options of the week)
--mail-from has no short version. This option was added to curl 7.20.0 in February 2010.
I know this surprises many curl users: yes curl can both send and receive emails.
SMTP
curl can do “uploads” to an SMTP server, which usually has the effect that an email is delivered to somewhere onward from that server. Ie, curl can send an email.
When communicating with an SMTP server to send an email, curl needs to provide a certain data set and one of the mandatory fields of data that is necessary to provide is the email of the sender.
It should be noted that this is not necessary the same email as the one that is displayed in the From: field that the recipient’s email client will show. But it can be the same.
Example
curl --mail-from from@example.com --mail-rcpt to@example.com smtp://mail.example.com -T body.txt
Receiving emails
You can use curl to receive emails over POP3 or IMAP. SMTP is only for delivering email.
Related options
--mail-rcpt for the recipient(s), and --mail-auth for the authentication address.