Emails that K9 automatically sends out: Temporary Password, Uninstall Notification, Email Change Verification and New Licenses.
You are not getting any of the automated emails from K9.
You may not receive email from K9 if you are using a Spam filter. If you are blocking spam, you may choose to block 100% of all mail from people or organizations that you don't know (including K9); in this case our communications cannot get through.
In some cases, the mail server will tell us that our message was blocked. However, many spam filters will simply drop the email when a predetermined threshold is reached. In many cases the spam service doesn't notify the sender OR the receiver that the spam was even handled.
Given this we recommend reviewing the following:
Do you have spam filtering on your email account, or does your ISP filter spam for you?
If so, we advise you to look through your spam mails to get the address. If located, please add "firstname.lastname@example.org" to your "always allowed" list of senders. In this way any email we send to you will be allowed through. Note that this is not something that we can do from our end.