Questions[sendmail](server)

I am having trouble in delivering mail to google from a fresh sendmail install on ubuntu 14.04. The DNS-records seem to be fine for the ip. Something else must be wrong.

Sending mail from command line:

sudo sendmail -v -Am -i [email protected];

Verbose output:

myname@fx1:/etc/mail$ sudo sendmail -v -Am -i [email protected];
[email protected]... Connecting to aspmx.l.google.com. via esmtp...
220 mx.google.com ESMTP v1si55415385wja.21 - gsmtp
>>> EHLO staging.mydomain.com
250-mx.google.com at your service, [2a01:4f8:212:27c8::2]
250-SIZE 35882577
250-8BITMIME
250-STARTTLS
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8
>>> STARTTLS
220 2.0.0 Ready to start TLS
>>> EHLO staging.mydomain.com
250-mx.google.com at your service, [2a01:4f8:212:27c8::2]
250-SIZE 35882577
250-8BITMIME
250-ENHANCEDSTATUSCODES
250-PIPELINING
250-CHUNKING
250 SMTPUTF8
>>> MAIL From:<[email protected]>
250 2.1.0 OK v1si55415385wja.21 - gsmtp
>>> RCPT To:<[email protected]>
>>> DATA
250 2.1.5 OK v1si55415385wja.21 - gsmtp
354  Go ahead v1si55415385wja.21 - gsmtp
>>> .
550-5.7.1 [2a01:4f8:212:27c8::2] Our system has detected that this message does
550-5.7.1 not meet IPv6 sending guidelines regarding PTR records and
550-5.7.1 authentication. Please review
550-5.7.1  https://support.google.com/mail/?p=ipv6_authentication_error for more
550 5.7.1 information. v1si55415385wja.21 - gsmtp
myname... Connecting to local...
myname... Sent

Any help is greatly apreciated. Thank you in advance.

I have Postfix setup on my server so that I can send outgoing mail using the command-line:

mail -s "Subject" [email protected]

1. Is this using Sendmail or Postfix ?
2. Is "Sendmail" just a software category or a distinct program ?
3. If something is "Sendmail-ready" does that mean it will work with Postfix ?

Everything I've read online seems to use these two terms interchangeably.

This is a canonical question about avoiding outgoing mail being classified as spam.
Also related:

• Fighting Spam - What can I do as an: Email Administrator, Domain Owner, or User?
• What are SPF records, and how do I configure them?

I'm wondering how to prevent my emails from my site being marked as spam? I'm using sendmail.

I'm trying to send emails through my ruby-on-rails application. The mails are all written in swedish (if that does make a difference?). I don't know why they keep getting marked as spam.

Are there any things that I can do to minimize the risk?

I can't send out emails,

need to look into the logs,

but where is the log?

When trying to start sendmail or send a mail using a wordpress plugin, this error shows up in the maillog:

"My unqualified host name (foo.bar) unknown; sleeping for retry"

After Googling the best advice was, "add foo.bar to the /etc/hosts file", but it already is:

127.0.0.1     localhost localhost.localdomain
127.0.0.1     foo.bar