very basis telnet commands for SMTP fail. it used to work a few weeks ago

[natasha1234567890]

~/mailhog$ telnet localhost 1025
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 mailhog.example ESMTP MailHog
ehlo ss.com
250-Hello ss.com
250-PIPELINING
250 AUTH PLAIN
mail from: ff@.com
550 Invalid syntax in MAIL command
rcpt to: qq@ss.com
500 Unrecognised command
data
500 Unrecognised command
.
500 Unrecognised command
quit
221 Bye
Connection closed by foreign host.

[DBX12]

I guess it is due to your MAIL FROM: ff@.com being invalid. If I remember correctly (and that is to be doubted since the spec for mail addresses is one historically grown dumpster fire), you cannot have a host part of .com only. I guess MAIL FROM: ff@com could be valid, at least in lab settings.

[natasha1234567890]

NO option for email domain works (tried ff.com, com, ff):

u:~$ telnet localhost 35
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
220 mailhog.example ESMTP MailHog
ehlo ff.com
250-Hello ff.com
250-PIPELINING
250 AUTH PLAIN
mail from: dd@ff.com
550 Invalid syntax in MAIL command
mail from: dd@ff
550 Invalid syntax in MAIL command
mail from: dd@com
550 Invalid syntax in MAIL command

[twisted1919]

 telnet localhost 1025
Trying ::1...
Connected to localhost.
Escape character is '^]'.
220 mailhog.example ESMTP MailHog
ehlo ss.com
250-Hello ss.com
250-PIPELINING
250 AUTH PLAIN
mail from: ff@what.com
550 Invalid syntax in MAIL command
mail from: <ff@what.com>
250 Sender ff@what.com ok

[here]

Observed while following this article on smtp over telnet https://www.redhat.com/sysadmin/telnet-troubleshoot-mail-system

The workaround described by twisted1919 works for me by adding <> surrounding the email address.

mail from: user@example.com
550 Invalid syntax in MAIL command
mail from: <user@example.com>
250 Sender user@example.com ok