Emails not queuing or spooling and stuck in pending

There are a handful of contacts that will not queue or spool to receive an email.

They go from queued, to pending but never sent.

When I look in the spool folder there is nothing there even though the job says it successfully sent.

php app/console mautic:broadcasts:send

STAFF - 02-21-2018 - 5 Free Downloads from Getty Music!
1/1 [============================] 100%

±---------------------------------------------------------------±-------±---------+
| Channel | # sent | # failed |
±---------------------------------------------------------------±-------±---------+
| Email: PC - 02-21-2018 - 5 Free Downloads from Getty Music! | 0 | 0 |
| Email: STAFF - 02-21-2018 - 5 Free Downloads from Getty Music! | 1 | 0 |
±---------------------------------------------------------------±-------±---------+