Redmine Notification Emails not sending

Question

I'm trying to get Redmine to send notification emails, but I can't seem to get it to work. I'm following the directions for email configuration on the Redmine site, but nothing seems to be working.

My configuration.yml Configurations are:

default:
  email_delivery:
    delivery_method: :smtp
    smtp_settings:
      enable_starttls_auto: true
      address: "smtp-relay.gmail.com"
      port: 587
      domain: "smtp-relay.gmail.com"
      authentication: :plain
      user_name: "[email protected]" # this is a G Suite account 
      password: "password"

Note that I enabled SMTP relay as described in the Redmine documentation.

I've tried:

1. Replacing "default" with "production"
2. Replacing "smtp-relay.gmail.com" with "smtp.gmail.com"
3. Using a totally different G Suite account under a different domain.
4. Using SMTP settings from an Office 365 account that I know work because I use them in Gmail.

Every time, when I go to send a test email from the Redmine interface, I get:

An error occurred while sending mail (execution expired)

Here's the Redmine info:

Environment:
  Redmine version                4.1.1.stable
  Ruby version                   2.6.6-p146 (2020-03-31) [x86_64-linux]
  Rails version                  5.2.4.2
  Environment                    production
  Database adapter               Mysql2
  Mailer queue                   ActiveJob::QueueAdapters::AsyncAdapter
  Mailer delivery                smtp
SCM:
  Git                            2.25.1
  Filesystem                     
Redmine plugins:
  no plugin installed

I'm running Ubuntu 20.04.1 LTS (GNU/Linux 5.4.0-48-generic x86_64) on Linode.

Thanks!