nauta.cu has very few storage and issues with message deletion

[r10s]

with #8240 we removed the config option delete_server_after for various reasons (eg. avoid corner cases server does smth else than client, avoid a whole set of bugs, align chatmail with classic, simplification in general). for most classic server, this change does not matter as they have enough space and/or can cleanup automatically, the setup is anyway much more complex than chatmail.

nauta, however, has few mb of storage only, in the past, for nauta, delete_server_after was set to "at once" automatically therefore. also there seems not to be an option to cleanup automatically in the web view

ftr, this broke multi-device usage for nauta. in retrospective, some of the reports of errors nauta has, might be related to that (eg. member added messages were not seen on other devices).

however, at least single-device usage was working by that option.

currently, at least i do not see extra code for nauta when it comes to deletion. meaning, that also in single-device-mode, messages are not deleted, as the deletion takes only place for chatmail. might totally be i missed smth. there is some confusion about that part, the question was raised in #8240 but stays unanswered, and in some chat was claimed there is some exception, cc @adbenitez
EDIT: confirmed by @link2xt that we do not do anything special for nauta

what can we do about that?

• leave things as is, point to chatmail
• add an exception to make nauta work with single-device mode (multi-device was always broken it seems) - we want to get rid of "Multi-device-mode option" as well, but until then, ppl can force deletion by setting single-device mode (which is also default)
• always delete encrypted messages in single-device-mode
• ...

[link2xt]

#8240 suggested that we treat nauta.cu as chatmail, this is the same as "add an exception to make nauta work with single-device mode". Basically we need to tweak should_delete_all_downloaded_messages to use is_chatmail || is_nauta instead of 'is_chatmail` as the condition. This will solve the problem for single-device nauta.cu setups only, but is an easy change.

All the logic for deleting messages is contained in delete_expired_imap_messages (there is one call to ephemeral::should_delete_all_downloaded_messages in download_msgs, but as the comment explains it is only for tests and should probably be removed:

core/src/download.rs

Lines 172 to 178 in c26b6a0

	if ephemeral::should_delete_all_downloaded_messages(context, session.is_chatmail()).await? {
	// Now that the message was downloaded, it likely needs to be deleted;
	// trigger a re-check by interrupting the inbox folder.
	// This is mainly needed to make the tests pass;
	// on real devices, it would be fine to delete the message at the next iteration.
	context.scheduler.interrupt_inbox().await;
	}

). We can also implement more complex logic in delete_expired_imap_messages, e.g. unconditional deletion after 20 days to support multi-device.

[r10s]

sounds good, to unblock the release an easy change seems to be good enough.

but would be great to have unconditional deletion and multi device support for small providers as nauta - that would be a clear signal that we improve here, and do not abandon classic email usage as relay. it is useful also for other provider - and probably also for the peace of mind otherwise.

from the chat, message from @iequidoo :

Can't we delete downloaded encrypted messages in the single-device mode immediately instead of the exception for nauta? Exporting keys isn't supported anymore anyway

assuming this is an comparable easy change -
is there anything speaking agains that?

[link2xt]

I opened #8283 to delete encrypted messages in single device case immediately.