I am testing a mail server,and,everywhere I read to end the data command with a period to signify the end of the data. However, I
can not seem to get this to work. Sample session follows:


250 ok
rcpt to: <nospam@test.com>
250 ok
data
354 go ahead
From: Test_sender <testmail@test.com>
To: Test_receiver <nospam@test.com>
Subject: Just a stupid SMTP test

Just a test !
.
.
.
quit

^.
^]
telnet> quit
Connection closed.

The single dot being an "end of file" character is historical.
Today terminals have a magic key; most common is Ctrl-d

99.999999+% of web-searches say it SHOULD work! (except 1 `nc` to gmail)

What 'terminal' are you doing this in? Post your output of: stty -a; uname -a

Maybe it's a 'cr/lf/nl' issue. (I used WinXP telnet!) What OS/MTA? On CentOS7, I get:
...
250 2.1.5 Ok
data
354 End data with <CR><LF>.<CR><LF>
.
250 2.0.0 Ok: queued as CA21A121D385
quit
221 2.0.0 Bye
Connection closed by foreign host.
You have new mail in /var/spool/mail/root
# netstat -tulpn | grep :25
tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN 1204/master
tcp6 0 0 ::1:25 :::* LISTEN 1204/master
# ps lww -p 1204
F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND
5 0 1204 1 20 0 93612 2160 ep_pol Ss ? 0:00 /usr/libexec/postfix/master -w

p.s. WELCOME! Best wishes...