linux - Gmail bouncing postfix mail

I followed this tutorial to get email working on my VPS. I've been having problems sending email to Gmail.

I can receive emails fine, but any mail that is sent to Gmail is bounced with the following message:

Our system has detected that this message
is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to
Gmail, 550-5.7.1 this message has been blocked. Please visit 550 5.7.1
https://support.google.com/mail/answer/188131 for more information.
qa9si13920205vdb.18 - gsmtp (in reply to end of DATA command)

I have updated my PTR record to match my IP address.

Before I was getting messages in mail.log that looked like this:

postfix/smtp[3160]: connect to gmail-smtp-in.l.google.com[2607:f8b0:400c:c06::1b]:25: Connection timed out

and after searching around I found that this was a problem with IPv6, which I've now disabled on my box. I've stopped getting these messages but I'm still receiving bounce messages.

Here is my main.cf:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version


# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname


smtpd_banner = $myhostname ESMTP $mail_name (Debian/GNU)
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h


readme_directory = no

# TLS parameters
#smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
#smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
#smtpd_use_tls=yes
#smtpd_tls_session_cache_database = btree:${data_directory}/smtpd_scache
#smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

smtpd_tls_cert_file=/etc/ssl/private/_com/ssl-bundle.crt

smtpd_tls_key_file=/etc/ssl/private/_com.key
smtpd_use_tls=yes
smtpd_tls_auth_only = yes
smtpd_tls_loglevel = 1

smtp_address_preference = ipv4

#Enabling SMTP for authenticated users, and handing off authentication to Dovecot
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth

smtpd_sasl_auth_enable = yes

smtpd_recipient_restrictions =
      permit_sasl_authenticated,
      permit_mynetworks,
      reject_unauth_destination

# See /usr/share/doc/postfix/TLS_README.gz in the postfix-doc package for
# information on enabling SSL in the smtp client.


myhostname = 
alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
#mydestination = .com, , localhost., localhost
mydestination = localhost
relayhost = 
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128
mailbox_size_limit = 0
recipient_delimiter = +

inet_interfaces = all
virtual_transport = lmtp:unix:private/dovecot-lmtp

#Virtual domains, users, and aliases
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-mailbox-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailbox-maps.cf
virtual_alias_maps = mysql:/etc/postfix/mysql-virtual-alias-maps.cf

Here are the logs I get when trying to send email to gmail:

Jun  5 11:27:52  postfix/master[5118]: terminating on signal 15
Jun  5 11:27:53  postfix/master[5326]: daemon started -- version 2.11.3, configuration /etc/postfix
Jun  5 11:28:09  dovecot: imap-login: Login: user=<@.com>, method=PLAIN, rip=127.0.0.1, lip=127.0.1.1, mpid=5346, TLS, session=<0w+B8MYXwQB/AAAB>
Jun  5 11:28:09  postfix/submission/smtpd[5347]: connect from localhost[127.0.0.1]
Jun  5 11:28:09  postfix/submission/smtpd[5347]: Anonymous TLS connection established from localhost[127.0.0.1]: TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)
Jun  5 11:28:09  postfix/submission/smtpd[5347]: 9A97B6241F: client=localhost[127.0.0.1], sasl_method=LOGIN, sasl_username=@.com
Jun  5 11:28:09  postfix/cleanup[5352]: 9A97B6241F: message-id=.com>
Jun  5 11:28:09  postfix/qmgr[5335]: 9A97B6241F: from=<@.com>, size=1032, nrcpt=1 (queue active)
Jun  5 11:28:09  postfix/submission/smtpd[5347]: disconnect from localhost[127.0.0.1]

Jun  5 11:28:09  dovecot: imap(@.com): Disconnected: Logged out in=912 out=460
Jun  5 11:28:09  dovecot: imap-login: Login: user=<@.com>, method=PLAIN, rip=127.0.0.1, lip=127.0.1.1, mpid=5357, TLS, session=
Jun  5 11:28:09  dovecot: imap(@.com): Disconnected: Logged out in=333 out=1227
Jun  5 11:28:09  dovecot: imap-login: Login: user=<@.com>, method=PLAIN, rip=127.0.0.1, lip=127.0.1.1, mpid=5358, TLS, session=
Jun  5 11:28:09  dovecot: imap(@.com): Disconnected: Logged out in=90 out=861
Jun  5 11:28:10  postfix/smtp[5354]: 9A97B6241F: to=<@gmail.com>, relay=gmail-smtp-in.l.google.com[74.125.141.26]:25, delay=0.95, delays=0.06/0.03/0.22/0.65, dsn=5.7.1, status=bounced (host gmail-smtp-in.l.google.com[74.125.141.26] said: 550-5.7.1 [      12] Our system has detected that this message is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to Gmail, 550-5.7.1 this message has been blocked. Please visit 550 5.7.1 https://support.google.com/mail/answer/188131 for more information. qa9si13920205vdb.18 - gsmtp (in reply to end of DATA command))
Jun  5 11:28:10  postfix/cleanup[5352]: 9003A62422: message-id=<20150605152810.9003A62422@>
Jun  5 11:28:10  postfix/qmgr[5335]: 9003A62422: from=<>, size=3474, nrcpt=1 (queue active)
Jun  5 11:28:10  postfix/bounce[5359]: 9A97B6241F: sender non-delivery notification: 9003A62422
Jun  5 11:28:10  postfix/qmgr[5335]: 9A97B6241F: removed

Jun  5 11:28:10  dovecot: lmtp(5362): Connect from local
Jun  5 11:28:10  dovecot: lmtp(5362, @.com): nFazJArAcVXyFAAALAfe6g: msgid=<20150605152810.9003A62422@>: saved mail to INBOX
Jun  5 11:28:10  postfix/lmtp[5361]: 9003A62422: to=<@.com>, relay=[private/dovecot-lmtp], delay=0.06, delays=0/0.02/0.01/0.03, dsn=2.0.0, status=sent (250 2.0.0 <@.com> nFazJArAcVXyFAAALAfe6g Saved)
Jun  5 11:28:10  dovecot: lmtp(5362): Disconnect from local: Successful quit
Jun  5 11:28:10  postfix/qmgr[5335]: 9003A62422: removed