Changing the "Mail check" interval

Arrrgggh.  Sort of what I thought - thanks!

One way to restrict Mail Check to ‘manual only’ (instead of once every hour) would seem to be with selection of the “Extended Tracking” mode.

That will extend the interval. But it will not actually stop the mail checks. Extended tracking has other side effects. Those might be undesirable depending on your use case.

During Extended Tracking, would the Mail still be checked each time a Track Point is sent? If, for example, a two hour interval is sent, would the Mini leave the Sleep Mode (to send the Track Point) and also check for messages every 2 hours?

DanBRThough the answer was given below, I am going to provide a link that provides a bit more detail. Please see the following How Often Does the inReach Mini Series Check For Messages.

Yes, you do get a "mail check" whenever the device actually SENDS something. This includes the "deferred" track points which will eventually be sent in Extended Tracking mode.

To be perfectly clear, the "mail check" associated with sending anything is piggy-backed on the acknowledgement to the sent item. In other words, when the device sends, the Iridium network comes back "OK, got that and sent it" or "OK, got that and sent it - and oh, by the way, you have a message(s). Here they are." There is no extra batter drain associated with this unless you DO have messages.

This is mechanically different from what happens when you do a manual check, or when the device does the automatic hourly check. In that case, the device sends a check message to the Iridium network - "Hey, got any messages for me?" Network comes back with either "Yes, here they are" or "No, not right now." This consumes battery power every time. It consumes more battery if you DO have messages.

The extended conversational mode mentioned in the KB article works by periodically doing the equivalent of a manual check.

The link provided contains the following:

“NOTE: The automatic, hourly mail checks cannot be disabled”

Is this true? Doesn’t the Extended Tracking Mode disable these mail checks?

It's hard to say. Some of the documentation indicates that "message listens are disabled". Others, like the one cited above, say that the automatic hourly checks cannot be disabled. 

In any case, the power cost of the hourly check is minor compared to the cost of the OTHER things that are disabled in extended tracking mode (for example, BT and ANT+ radios, screen use). The real risk to the hourly check is that it will occur in challenging conditions. In this case, the device retries the mail check repeatedly - which can be a real battery suck. The moral of the story is "do not bury the device in your pack while powered up". And try to maintain a decent sky view whenever possible.

That is true you cannot disable them as there is no options that allow you to change or disable them. However, you are correct that extended traking mode when you choose to turn it on will automatically turn them off. Extended Tracking and Expedition Modes on Garmin inReach Products. 

The difference between the articles is that you will not have the option to disable the listen interval unless the device does it through another mode.