Permissions issue accessing spool file when sending emails

Using OTP release 2.5.0 on Debian 11 (bullseye) Mailer configured with Sendmail using exim4 4.94.2

I am unable to get Pleroma to send any emails successfully. Password resets for example do not work.

When I run pleroma_ctl email test --to my@email.com, a success message is printed, but no email actually goes out, and no logs appear in /var/log/exim4. However, I do see the following journalctl entry logged several times for each attempt:

Jan 02 23:25:01 localhost pleroma[507382]: 2023-01-02 23:25:01 1pCUAv-0027za-OH Failed to create spool file /var/spool/exim4//input//1pCUAv-0027za-OH-D: Permission denied

This seems like maybe something funky going on with my system, and not an actual issue with Pleroma. Although I will point out that emails do send successfully when I run su pleroma sendmail my@email.com < test-email.txt.

Here's my mailer config:

config :pleroma, Pleroma.Emails.Mailer, [ adapter: Swoosh.Adapters.Sendmail, cmd_path: "/usr/sbin/sendmail", enabled: true, cmd_args: ""]