How do I deliver an email stuck in my Postfix mail queue?

Question

How do I send this email from Postfix? I am using CentOS release 6.8 running Postfix 2.6.6.

maillog

Jan 16 21:23:16 ip-172-99-99-99 postfix/smtp[17128]: connect to alt1.aspmx.l.google.com[2607:f8b0:4001:c06::1a]:25: Network is unreachable
Jan 16 21:23:16 ip-172-99-99-99 postfix/smtp[17128]: connect to aspmx2.googlemail.com[2607:f8b0:4001:c06::1a]:25: Network is unreachable
Jan 16 21:23:16 ip-172-99-99-99 postfix/smtp[17128]: connect to aspmx3.googlemail.com[2607:f8b0:4002:c03::1a]:25: Network is unreachable
Jan 16 21:23:16 ip-172-99-99-99 postfix/smtp[17128]: connect to aspmx5.googlemail.com[2607:f8b0:400c:c11::1b]:25: Network is unreachable
Jan 16 21:23:16 ip-172-99-99-99 postfix/smtp[17128]: connect to aspmx.l.google.com[2607:f8b0:400e:c04::1a]:25: Network is unreachable
Jan 16 21:23:16 ip-172-99-99-99 postfix/smtp[17128]: A3AEE2026D: to=<[email protected]>, relay=none, delay=361752, delays=361752/0.04/0.28/0, dsn=4.4.1, status=deferred (connect to aspmx.l.google.com[2607:f8b0:400e:c04::1a]:25: Network is unreachable)

Queue

# postqueue -p
-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
A3AEE2026D     9899 Thu Jan 12 16:54:04  [email protected]
(connect to aspmx4.googlemail.com[2607:f8b0:400d:c0b::1a]:25: Network is unreachable)
                                         [email protected]

-- 11 Kbytes in 1 Request.

Ping

# ping alt1.aspmx.l.google.com
PING alt1.aspmx.l.google.com (74.125.202.26) 56(84) bytes of data.
64 bytes from io-in-f26.1e100.net (74.125.202.26): icmp_seq=1 ttl=32 time=50.7 ms

Answer 1

postqueue -f is generally used to flush the queue, after the root cause of the delivery failure is solved.

-f     Flush the queue: attempt to deliver all queued mail.

       This option implements the traditional "sendmail -q" command, by
       contacting the Postfix qmgr(8) daemon.

       Warning: flushing undeliverable mail frequently will  result  in
       poor delivery performance of all other mail.

postqueue -i can be used for a specific message:

-i queue_id
      Schedule  immediate delivery of deferred mail with the specified
      queue ID.

      This option implements the traditional sendmail -qI command,  by
      contacting the flush(8) server.

      This feature is available with Postfix version 2.4 and later.

If you have a permanent IPv6 outage, you may disable IPv6 in postfix with inet_protocols.

From http://www.postfix.org/IPV6_README.html :

/etc/postfix/main.cf:
    # You must stop/start Postfix after changing this parameter.
    inet_protocols = ipv4       (DEFAULT: enable IPv4 only)
    inet_protocols = all        (enable IPv4, and IPv6 if supported)
    inet_protocols = ipv4, ipv6 (enable both IPv4 and IPv6)
    inet_protocols = ipv6       (enable IPv6 only)