After working fine for a while, since a couple of months our tablet cannot send mails from mail accounts across several providers. However, receiving mails works. I tried whatever I could think of or found on the internet (see below), and I am quite desperate... This page shows several possibly related questions, but they do not describe my problem.
It says "sending ..." -> Error message "senden fehlgeschlagen" = sending did not work. Update: Sometimes (seems random, possibly because it is shown for short time ~ 1 sec) it also says in addition "Server nicht verfügbar" = server not accessible (although internet and smtp server work when tested from the other devices, see below).
- Samsung Galaxy 10, 2014 edition Android 5.1.1, Safety patch 2017-04-01 (i.e. all regular updates offered for it)
- has enough memory > 6 GB free
- mail client: standard Android mail client
- mails are managed via IMAP (not POP3) / SMTP
Mail providers tested:
- web.de (2 accounts from 2 people)
- tested each time with only one single account set (and all others removed), just to make absolutely sure the do not interfere with each other
What DOES work is the following:
- sending (and every else) mails from each of the accounts using a) another android device (Samsung Galaxy phone, Android 5.0.1 - i.e. all regular updates offered for that device), b) PC/Thunderbird, and c) webmail.
- send & receive mails via POP3. I wish to use IMAP (PORT numbers adjusted, same settings exp. for outgoing (SMTP) server).
- internet bandwidth (45 MBit/s download, 6 Mbit upload, ping 92 ms) and volume
What I tried so far, without success:
- shut down and restart the device
- double-check mail account settings (incoming: imap.web.de / imap.mail.de, SSL, port 993, optional imap path prefix: none; outgoing: smtp.web.de / smtp.mail.de, TLS, port 587, "Anmeldung erfordern" = need authentification checked in checkbox, same PW). All is set as suggested by the respective providers, and as set in the other android device from which I can send mails.Tried also alternative settings (e.g. SMTP: port 25, and other settings), but this did not improve anything (even though probably not all possible combinations)
- Removed and re-created the accounts (only one at a time). Still can receive, but not send.
- Tried another WiFi at a friend's home, different telecommunication provider, same problem. There is no problem with bandwith, internet volume etc.
- Tried on multiple days since several weeks to months
- Mail app is updated
I prefer the normal android client. To our knowledge, there is no other (possibly interfering) client installed.
As suggested in comment below (thanks!): deleted all data and deleted all cache from mail app (and again deleted and re-created account) - no change.
- No certificates are needed, but the mail provider requests the users to specifically allow mail clients (mail clients/apps in general, i.e. management via IMAP/POP3, as opposed to the provider's web surface). This option has always been and is still chosen (doublechecked, and works from other devices).
Thanks in advance, I am looking forward to your help.