Hi @guyou,
I see you asked this Upgrade to Bookworm Impossible on armel and it is where you were told armel is not more supported when upgrading to bookworm.
Your Excito B3 is based on a Marvell 88F6281 which is ARMv5TE-compliant then armel. This is 32bit old arm, since then ARMv7 with armh came and nowadays all is 64bits. Even armh support start to disappear…
When i look for it, It look like it has never been really supported widely, from this topic What would be necessary to have build for armel platform it is told that it is a matter of finding contributors …
On the other hand Yunohost mail is based on postfix for mail so upgrading only postfix might be enough to continue to support it but by losing any fancy support of users… This is now a matter of removing the yunohost layer and relying only on debian… Not sure if there is so much documentation on how to fall back to debian.
As you see i don’t really come with answers, i just digged in your question and added some context…