Emails undeliverable to Yahoo and Outlook - DMARC rejection

[Beardmancer]

I have one contact with an Outlook address that has been undeliverable for awhile, which I just attributed to Microsoft being picky. Recently, however, two other contacts with Yahoo addresses have been undeliverable for me as well.

Outlook rejection:

Access denied, sending domain [IANTOMPKINS.COM] does not pass DMARC verification and has a DMARC policy of reject.

Yahoo rejection:

This mail has been blocked because it failed authentication checks against the sending domains DMARC policy.

According to my Cloudron dashboard everything is good, although IPV6 checks are not green (is that an issue?):

The site mail-tester.com didn't find any issues. However, the site mxtoolbox.com says my DKIM record is not published:

Results from cloudron-support --troubleshoot:

[OK] Root disk usage is OK (41%)
[OK] Memory usage 1s OK (55%)
[OK] Clock is NTP-synchronized
[OK] node version is connect
[OK] IPv6 is enabled in kernel. No public IPv6 address
[OK] docker is running
[OK] docker version is connect
[OK] MySQL is running
[OK] netplan is good
[OK] DNS is resolving via systemd-resolved
[OK] is running
[OK] IPV4 HTTPS to api. cloudron.io/api/v1/helper/public_ip
[SKIP] IPV6 HTTPS api.cloudron.1o/api/v1/helper/public_ip - no public IPv6
[OK] auth.docker.io/token
[SKIP] auth.docker.io/token - no public IPv6 address
[OK] IPV4 HTTPS acme-vo2.api.letsencrypt.org
[SKIP] IPv6 HTTPS to acme-v02.api.letsencrypt.org - no public IPv6 address
[OK] nginx is running
[OK] dashboard cert is valid
[OK] dashboard is reachable via loopback
[OK] No pending database migrations
[OK] Service mysql' is running and healthy
[OK] Service 'postgresal' is running and healthy
[WARN] Service 'mongodb' is not running (may be lazy-stopped)
[OK] Service 'mail' is running and healthy
[OK] Service graphite is running and healthy
[OK] Service 'sftp' is running and healthy
[OK] box v9.2.0 is running
[OK] Dashboard is reachable via IPv4 (https://my.iantompkins.com)
[SKIP] Dashboard IPv6 reachability - no public IPv6 address
[OK] Domain iantompkins.com is valid and has not expired address
======== Summary ========
PASS: 26
WARN: 1
FAIL: 0
SKIP: 4
Warnings:
- Service 'mongodb' is not running (may be lazy-stopped)

I'm very much a novice on this and I'm not sure where to look next. What can I do to troubleshoot? I am not using a relay and would prefer not to if possible.