e-mail notifications stopped working

[Inrumpo]

Expected behavior

After releasing an episode, an automatic e-mail will be sent to contributors.

Actual behavior

No e-mails will be sent anymore.

Additional info

This isse is based on this topic over at the Podlove community.

This has worked for me just fine right after release of this feature in 2.6.0. Somewhere down the road this stopped working.

I've tried with no luck:

• tested different episode
• used different sender
• tested different recipients
• checking junk-mail folders
• changed roles and groups
• checked for PHP errors in error_log files
• checked e-maillog
• Podlove repair button & clearing caches
• deactivated and reactivated the mail notifications module

Other mail notifications are still working.
Podlove Jobs are running.

The Podlove debug log shows me this (example with contributor named Sebastian):
Tried sending email notification to Sebastian. wp_mail was unable to send.

Details:

---
module: E-Mail Notifications
contributor_id: "19"
contributor_name: Sebastian

System information (see Podlove > Support menu)

Website https://GameTalk.FM
PHP Version 7.0.23
WordPress Version 4.8.2
WordPress Theme Joeys Twenty Fifteen Child v1.0
WordPress Database Charset utf8
WordPress Database Collate
Publisher Version 2.6.2
Web Player Version no web player found
Twig Version 1.33.2
open_basedir ok
curl Version 7.54.0
iconv available
simplexml ok
max_execution_time 50
upload_max_filesize 100M
memory_limit 256M
disable_classes
disable_functions exec, shell_exec, system, dl, passthru, proc_open, proc_close
permalinks ok (/%postname%/)
podlove_permalinks ok
podcast_settings ok
web_player ok
podlove_cache on
assets
  - mp3 audio/mpeg https://GameTalk.FM/feed/mp3/
  - m4a audio/mp4 https://GameTalk.FM/feed/m4a/
cron ok

0 errors
0 notices
Nice, Everything looks fine!

[eteubert]

Likely fixed in 3a43778. There was some trouble rendering the message, resulting in an empty message body, resulting in a failed attempt to send the message.

I also added more verbose debugging information should issues occur again.

[Inrumpo]

Test mails are working again. This issue seems to be fixed. Thanks!