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From: VanguardLH <V@nguard.LH>
Newsgroups: comp.mobile.android
Subject: Re: Android 11: App polling interval is not 15 minutes minimum?
Date: Sat, 9 Mar 2024 12:41:02 -0600
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Andy Burns <usenet@andyburns.uk> wrote:

> Andy Burns wrote:
> 
>> I'll leave it idle for a while (I think I have it set for 24 minutes) 
>> and retry.
> 
> The phone has been idle for an hour, sitting undisturbed on a bedside 
> table (i.e. no body movement waking it).  I sent another email and got 
> notified by K9 within seconds ...

Yep, your e-mail provider supports IMAP IDLE.  That doesn't wait for a
poll interval to detect new messages are available.  Alas, many users
report IDLE isn't super-reliable.  They get a new message in the Inbox
on the server, and they don't get notified in their client until the
next mail poll.  It's a nice feature, but not 100% reliable.  In
addition, the server can disconnect after 29 minutes, so it isn't
reestablished until the next mail poll.

https://joshdata.wordpress.com/2014/08/09/how-bad-is-imap-idle/

https://datatracker.ietf.org/doc/html/rfc2177, section 3.
   The server MAY consider a client inactive if it has an IDLE command
   running, and if such a server has an inactivity timeout it MAY log
   the client off implicitly at the end of its timeout period.  Because
   of that, clients using IDLE are advised to terminate the IDLE and
   re-issue it at least every 29 minutes to avoid being logged off.
   This still allows a client to receive immediate mailbox updates even
   though it need only "poll" at half hour intervals.

I don't remember seeing an IMAP IDLE capable client that lets you
configure when it times out an IDLE connect to disconnect and reconnect
to get another half hour before a timeout.  Apparently K9 has a
24-minute timeout on IDLE connections hoping to avoid server-side IDLE
timeouts (assuming it has not been shortened on the server), but the
server can still decide to expire IDLE connections for other causes.
Plus, the network route between client and server may falter.

Alas, IMAP IDLE only works on the Inbox folder, not on other folders.
If the server's anti-spam filtering moved a message into your Junk
folder, you're reliant on mail polling to get notified of false
positives deposited in a non-Inbox folder.  The false positive isn't in
your Inbox at any time, so IMAP IDLE won't detect you got the new
message.

You should have your e-mail client configured to do polling.  If the
server supports IDLE, your client can get new messages in the Inbox very
quickly, but not in other folders.  For the other folders, polling gets
used.

To what minimum interval can you configure K9 to poll?  The latest
version has a minimum of 15 minutes, and why K9 users are complaining
about the longer poll interval.  The old version let you set it down to
1 minute.  I don't know if it was the Feb 29 update to 6.800 that
changed to the 15-min min poll interval, or a slightly older version
that changed the minimum.  

I don't use K9, but was interested in hearing *Android* forces a minimum
polling interval to conserve battery power.  Wonder if you exclude the
e-mail app if the min poll interval is not enforced, but that would be a
battery power saving setting, so what if you don't use battery saving
mode where exclusions wouldn't apply?