I'd still go with a calendar for super important periodic stuff. I believe that most email services use at least a two level approach to spam filtering.
1. First, they do some filtering at the SMTP stage to detect spammers and drop the mail.
2. Mail that doesn't get rejected at the SMTP stage then goes through the delivery process to deliver to your account. This is where your filters have a say in what happens.
Here's Fastmail's description of the SMTP stage filtering [1].
I wouldn't want to miss something important because the sender happened to misconfigure their mail system after an update in a way that trips the receiving side's SMTP stage filters.
1. First, they do some filtering at the SMTP stage to detect spammers and drop the mail.
2. Mail that doesn't get rejected at the SMTP stage then goes through the delivery process to deliver to your account. This is where your filters have a say in what happens.
Here's Fastmail's description of the SMTP stage filtering [1].
I wouldn't want to miss something important because the sender happened to misconfigure their mail system after an update in a way that trips the receiving side's SMTP stage filters.
[1] https://www.fastmail.help/hc/en-us/articles/360060591393