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I am trying to use SENDMAIL (v8.15) on a Pi in my network to just forward mails to my SendGrid account. This is needed because my legacy webcams on my network cannot use the very long password required by SendGrid.

The basic SENDMAIL is working, but it is not using AUTH LOGIN when connecting to SendGrid. I have installed the sasl2-bin package. How do I "link up" SENDMAIL to use the SASL installed on the machine? Is SASL even needed when SENDMAIL is operating as a client in this case?

My authinfo file contains:

 AuthInfo:smtp.sendgrid.net "U:api.key" "P=cGFzc3dvcmQ=" "M:LOGIN PLAIN"

Amost everything else is out of the box except the following in my sendmail.mc file:

FEATURE(`authinfo')
define(`RELAY_MAILER_ARGS',`TCP $h 25')dnl
define(`SMART_HOST',`smtp.sendgrid.net')dnl
define(`confAUTH_MECHANISMS',`EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN')dnl
define(`confAUTH_OPTIONS',`A')dnl

After rebuilding and restarting, I am still getting:

AUTH=client, available mechanisms do not fulfill requirements

AUTH=client, relay=smtp.sendgrid.net., temporary failure, connection abort

stat=Deferred: Temporary AUTH failure.

I traced the traffic with TCPDUMP, and saw that after SendGrid's EHLO's response of:

250-smtp.sendgrid.net
250-8BITMIME
250-PIPELINING
250-SIZE 31457280
250-STARTTLS
250-AUTH PLAIN LOGIN
250 AUTH=PLAIN LOGIN

the Pi sends a QUIT command. It didn't attempt AUTH LOGIN.

What is needed to make SENDMAIL, acting as a client, to use AUTH LOGIN?

1 Answer 1

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Besides sasl2-bin, there is a need to also install libsasl2-modules.

I found detailed instructions at http://memoryslipping.blogspot.com/p/sendmail.html.

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  • The above worked for me too, it needed sasl2-bin AND libsasl2-modules. Running Armbian linux on a Pine64, but the info seems applicable. Commented Jun 18, 2021 at 20:03

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