Comments by DaveWelsh (Top 2 by date)

DaveWelsh 16-Aug-13 13:50pm View

I think the problem is that my server only accepts the PLAIN authentication method and I probably need something like NTLM or CRAM-MD5 enabled for the System.Net.Mail.SmtpClient to authenticate.

DaveWelsh 16-Aug-13 12:46pm View

Thanks jkirkerx,

I tried a few things:

1) I lowered the minimum required cipher strength to "low" by adding this line to my /etc/postfix/main.cf:

smtpd_tls_mandatory_ciphers = low

This didn't have any effect that I could detect.

2) I left the cipher strength at low and I tried changing the encryption protocol from TLSv1 to SSLv3 by adding this line of code:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Ssl3;

This resulted in a different line in my log file:

Aug 16 16:23:11 mail postfix/smtpd[31507]: Anonymous TLS connection established from unknown[a.b.c.d]: SSLv3 with cipher RC4-SHA (128/128 bits)

But the server still didn't authenticate me.

3) I tried authenticating without encryption enabled. This is what the log showed:

Aug 16 16:24:49 mail postfix/smtpd[31507]: connect from unknown[a.b.c.d]
Aug 16 16:24:49 mail postfix/smtpd[31507]: NOQUEUE: reject: RCPT from unknown[a.b.c.d]: 554 5.7.1 <dave@xxx.com>: Relay access denied; from=<administrator@xxx.com> to=<dave@xxx.com> proto=ESMTP helo=<amsterdam>
Aug 16 16:24:49 mail postfix/smtpd[31507]: lost connection after RCPT from unknown[a.b.c.d]
Aug 16 16:24:49 mail postfix/smtpd[31507]: disconnect from unknown[a.b.c.d]

So I'm starting to think that the .Net code is not even trying to log in.