Noticed today that I couldn’t send an MMS picture on the Messages app today, until I cropped it down significantly. Has anyone else observed this issue before? Haven’t really nailed down a size it needs to be under or anything like that, seems maybe I have to get it around 2mb or so?
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I don’t use QKSMS but have you tried sending the same photo using a different messaging app? This might be a way to start troubleshooting for an answer.
Seems a few people have a similar issue.
So if the bug is in QKSMS, then it’s probably also in /e/'s Message app which is a fork of QKSMS.
In which case I would expect the fix to come from upstream (i.e. from QKSMS, not from /e/) and to appear in Message app when /e/ merge the upstream version containing the fix. Unless /e/ have the time to investigate, provide a fix and send it back upstream, but I guess they will be more focussed on any issue in their own code.
Looking at the GitHub it looks like it was fixed in 3.8.1? And /e/ uses 3.7.1. So I guess we wait for next update?
Sorry for slow response. Been having some injury issues.
You could be in for a long wait 
. QKSMS 3.8.1 was released on 28 Jan 2020, and the latest release in F-Droid is 3.9.4. It doesn’t look like /e/ plan to move to a more recent release any time soon. You could maybe create an issue in /e/'s GitLab but I don’t know whether /e/ would take any action.
Easier just to install QKSMS and use that instead of /e/'s outdated fork I’ve been doing that for quite a while now, as I see no reason to use 21 month old code, and /e/'s version offers no advantages for me over upstream.