Mautic says 'emails sent', but nothing has actually gone out

Working on this again this weekend, trying to restart my business from another stand-still. Sent out another mailing to a small test segment of other email addresses I own - gmail etc. Nothing arrives. No errors in logs.

Trying to force sending from command line with php bin/console mautic:emails:send gives this error:

In ProcessEmailQueueCommand.php line 141:

  rename(): supplied resource is not a valid Stream-Context resource

mautic:emails:send [--message-limit [MESSAGE-LIMIT]] [--time-limit [TIME-LIMIT]] [--do-not-clear] [--recover-timeout [RECOVER-TIMEOUT]] [--clear-timeout [CLEAR-TIMEOUT]] [--lock-name [LOCK-NAME]] [--bypass-locking] [-t|--timeout TIMEOUT] [-x|--lock_mode LOCK_MODE] [-f|--force] [-h|--help] [-q|--quiet] [-v|vv|vvv|--verbose] [-V|--version] [--ansi] [--no-ansi] [-n|--no-interaction] [-e|--env ENV] [--no-debug] [--] <command>

What is this rename() function? Where is it used in the process? How can I find out?

When I use ls | wc as suggested by @joeyk I get this as response:

26      26     309

What does that mean? If 26 or 309 is the number of emails in the pool/queue (?) that is way more than I would expect.

With php bin/console mautic:messages:send I get this response:

Processing message queue
Messages sent: 0

The rename() error is also mentioned here and here - will research there further…