What is Marketing/Standard mail, and how long does it take to be delivered?
When we send letters via USPS Standard Mail (years ago called Bulk Mail, as of 2017 called Marketing Mail) it is hard to predict when the letter will arrive because the delivery standards are not the same as they are for First-Class mail. We've seen letters delivered in as little as 2 days and letters delivered in more than 10 days. Generally speaking you should see letters being delivered between 5 and 10 business days. If you happen to notice that a few of your letters took longer than that to be delivered, we wouldn't be surprised.
We certainly wouldn't recommend the use of Standard Mail for time sensitive mail, but its not a bad option for general information. Also the USPS does not allow the use of Standard Mail for bills, statements and recipient-specific information.