Helo

I have configured sendmail on my slackware server with STARTTLS - PLAIN authentication only.
I mean, the result of the EHLO command is:

250-ENHANCEDSTATUSCODES
250-PIPELINING
250-8BITMIME
250-SIZE
250-DSN
250-ETRN
250-STARTTLS
250-DELIVERBY
250 HELP

But when I try to send email to hotmail email addresses I get this log in mail.log:

AUTH=client, relay=mx1.hotmail.com., temporary failure, connection abort
msgIDxxxxxxxx: AUTH=client, available mechanisms do not fulfill requirements
... dsn=4.0.0, stat=Deffered: Temporary AUTH failure


This is repeated on each MX on hotmail.

How can I fix this?

What authentication can be needed at this level?, when my server authenticates its user and its trying to deliver the message to another server.
I thought that at this level the connected server checks only the PTR record if it is the same as presented by the server / or checks the spam black lists for match.

I have no idea what authentication it needs.

I was thinking about, maybe the connected server is checking if the server supports AUTH-entication and if it does not get this option in the response of EHLO command it supposes it is an open relay server. It is that possible??

I use PLAIN authentication but only after STARTTLS.