zen wrote: Thank you for your help, Kyle.

I'm not quire sure if I understand what that option "But do not send message if it's later than:" mean.

Does it mean "do not sent the message if the set send date is later than xx"?

That option is there to make sure that when a problem occurs with a missing cron execution (for example) late messages are not sent.

For example, lets say that a you scheduled to send a message X days before a subscription ends. And lets say that something happens and the cron job skips/fails and is not executed when it should.

Mailers have cut off dates. Configure "But do not send message if it's later than:" as needed. For example if I've a mailer configured to send 1 month before expiration and 1 month after then anywhere within that timeframe if I trigger the mailer it'll send fine. Mailers can also have send per customer or globally conditions, which can be adjusted with "Maximum messages per customer (0=unlimited):" and "Maximum messages in total (0=unlimited):".

Be sure you're using the correct mailer URL. 1 will prepare the queue and another will process it. There's also a 3rd URL that can do both. It won't resend to an email address if they're already in the queue. Your mail server may also reject the queue if you're sending too many emails (some have daily, weekly, or monthly limits; contact your host for limits) and may need to ensure CBSubs Mailer is configured to send in smaller batches (see CBSubs > Settings > Mailer).