Code snippets for Un-subscription Kerfuffle

mail.log

5.7.1 550-5.7.1 [2600:3c03::f03c:91ff:fe55:a961] Our system has detected that this
550-5.7.1 message does not meet IPv6 sending guidelines regarding PTR records
550-5.7.1 and authentication. Please review 550-5.7.1
https://support.google.com/mail/?p=IPv6AuthError for more information 550 5.7.1 .
g67si1934521qkd.67 - gsmtp

mail2.log

Sep 16 11:52:19 ubuntu postfix/smtp[31725]: 53ECE401AF: to=,
relay=aspmx.l.google.COM[74.125.22.27]:25, delay=0.41, delays=0.05/0/0.15/0.21,
dsn=2.0.0, status=sent (250 2.0.0 OK 1474041166 k10si6150203qkh.326 - gsmtp)

main.cf

# Gmail IPv6 retry:

smtp_reply_filter = pcre:/etc/postfix/smtp_reply_filter

original_smtp_reply_filter.sh

# Convert Google Mail IPv6 complaint permanent error into a temporary error.
# This way Postfix will attempt to deliver this e-mail using another MX
# (via IPv4).

/^5(\d\d )5(.*information. \S+ - gsmtp.*)/ 4${1}4$2

smtp_reply_filter.sh

# Convert Google Mail IPv6 complaint permanent error into a temporary error.
# This way Postfix will attempt to deliver this e-mail using another MX
# (via IPv4).
#/^5(\d\d )5(.*information. \S+ - gsmtp.*)/ 4${1}4$2
# Fix for September 2016 update for IPv6 failures

/^5(\d\d )5(.*. \S+ - gsmtp.*)/ 4${1}4$2