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Old 09-09-2004, 12:34 PM   #1
Registered: Oct 2003
Posts: 78

Rep: Reputation: 15
"User Unknown" error with Sendmail

Hello Everybody,

I am getting following problem when :

1. I connect to "" on port 25 using "telnet"

2. I am sending "MAIL FROM: <>"
gettting back "250 2.1.0 <>... Sender ok"

3. I am sending "RCPT TO: <>"
gettting back "250 2.1.5 <>... Recipient ok"

4. I am sending "RCPT TO: <>"
getting back "550 5.1.1 <>... User unknown"
response from the SMTP server.

But both the users (user A, user B) exists on the system "".

Can anybody please explain why this could have been happening??

Thanks in advance,

Last edited by girish_hilage; 09-10-2004 at 07:15 AM.
Old 09-09-2004, 10:01 PM   #2
Registered: Aug 2004
Location: Scotland
Distribution: Debian, Suse, Knoppix, Dyna:bolic, Mandrake [couple of years ago], Slackware [1993 or so]
Posts: 150

Rep: Reputation: 15
no idea but you identified yourself there li*txe... etc which did not seem to be your intention, as you changed the names elsewhere.
Old 09-10-2004, 04:14 AM   #3
Registered: Oct 2003
Posts: 78

Original Poster
Rep: Reputation: 15
Sendmail is not giving any error if I create users with names (a, b) in small letters on a system to which I am connecting.

The system to which I am connecting to is RH7.3 with rpm "shadow-utils-20000902-7" on it and the command
# useradd A
can create the user A (capital letter) successfully.

But on a system with RH9.0 with rpm "shadow-utils-4.0.3-6" on it gives error :
# useradd A
useradd: invalid user name 'A'

* Why the linux system user names are not allowed with 'Capital letter' in it??
* Is it due to this problem why sendmail was saying "User Unknown" Or could there be some other reason??

Old 09-10-2004, 07:10 AM   #4
Registered: Oct 2003
Posts: 78

Original Poster
Rep: Reputation: 15
now(after creating users "a", "b") both the commands :

"RCPT TO: <>"
"RCPT TO: <>"

to the SMTP server are working.

So does this mean that "sendmail" converts the recipient address to "lower case" ??
Hence when earlier there were users (A, B) [capital letters] on the system and I was sending the above headers then due to "lower case conversion" it might not have been finding the mailboxes (a, b) on the system.
If any other reasons please mail ...



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