Finding why outbound mail is delayed

Running postfix-3.2.4 here on Slackware-14.2. I am a professional services
sole practitioner, not a professional system or network admin.

After several years having outbound mail forwarded through my ISP's mail
server I changed ISPs and now have a static IP address. The other recent change
here is replacing the old Netgear FVS318 router with a Ubiquiti EdgeRouter-X
fast enough to take advantage of the 15/5Mbps speeds of my fiber connection.

Since the end of last week I find many messages delayed 1-2 days; several
hundred are listed in logwatch's daily report. These delayed messages
include may body_check rejections. However, since Friday pflogsumm is also
delayed rather than delivered. There are now 2 messages in the mail queue:

# mailq
-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
5E148991FE 182118 Mon Nov 13 03:10:26 root
<a href=""></a>

EF1E2991FD 815 Mon Nov 13 06:59:09 <a href=""></a>
(connect to AAAAA.AAAAA.AAA[DDD.DDD.D.DD]:25: Connection timed out)
<a href="mailto:mail-list- ... at mail dot">mail-list- ... at mail dot</a>

The output of postdconf -Mf is attached. So is the output of the DDD log
generated after I modified by appending '-D' to the smtp line.

I need to learn how to locate the source of this problem and how to fix
it. If more information is needed let me know and I'll provide it.