Sent SMS have a too short validity period

Hello,

I own a PinePhone and have been testing various Linux distributions and user interfaces on it this year. Phosh is currently the most usable Linux phone UI in my opinion (thanks for your work!), but there is an issue with SMS that prevents me to rely on it for messaging:

If I send a text to a phone that's offline, the expected behaviour of any SMS service is that the message is temporarily stored by the carrier, and when the receiver phone is later brought online, it gets the message delivered. The temporary storage should be as long as possible, so that the recipient still gets the message even if it's days later. This works as expected on iOS, Android, Plasma Mobile, sxmo, etc. but unfortunately not with Chatty (on either Phosh or Gnome Mobile). Here, sent messages have a validity period of about 2h (estimation from my tests) and are discarded afterwards.

I couldn't find a way to change this setting. This is quite problematic, because I regularly want to send information to people that may have their phone turned off and need to be sure they'll get the information.

Could you please either provide a way to set the SMS validity period, or do like others do (and like most users will expect it to be) and use the maximum validity period by default?

Thanks for your consideration!

P.S. This issue was first mentioned on the Pine64 forum (https://forum.pine64.org/showthread.php?tid=18203). At first I thought it was a ModemManager bug, because I had the same issue on various distributions, but later realised it was specific to Chatty; SMS sent from Spacebar (Plasma Mobile) and sxmo do have the expected long validity period and are properly distributed days later.