Sometimes, you see things you just want to refuse to believe.
While it is true that most problems and quirks of software or hardware are due to really profound reasons and can be fixed quickly, sometimes you just cannot find them easily, if something unexpected happend - something which you never even thought of or you just found to be impossible.
My gamechanger - for the WORST - has been Telekom, which I happily would like to propose for the next BigBrother Award:
To cut a long story short: A friend of mine did order an Webhosting Account at all-inkl.com - and this did work without any problem.
I did configure some Domain Redirection, Mail Accounts, included them to the Android Phone of that friend - everything was working just fine.
However, as soon as the person arrived at home, Mail did not work anymore on the phone.
After trying to track down the problem for far too long, I did call the (very nice) support and got some immediate help:
"Are you using a Telekom Line?" - well... Yeah? - "Oh.. Well, they include SMTP Whitelists in the new routers, to stop spammers and we are not on this whitelist... So you can recieve but not send mail..." - WAIT. WHAT?!
A quick check on the WIFI Symbol, IP Range of the Phone and an Network IP DOT 1 in the friendly browser later - "Speedport W724v - What can I do for you?" - Well, [D|F|S][a-z][a-z][a-z]!
Turns out, the new W724V, Entry 2 and Hybrid Home Routers of the Telekom "feature" an SMTP Server WHITELISTE. So if you try to use your nice myname.de SMTP Server - nop'! You have to include your own Servers to that list, otherwise connection will be blocked - regardless if you try to communicate via Port 25 or 587 via SSL or encrypted formats. Really, hot, bad, nasty stuff.
One could mention that fighting spamers is a good idea, but this approach is as china-like as it is 1984.
So, kudos Telekom - you just made it impossible for "non-IT people" to use their own not Telekom and al. hosted SMTP service!
More can be found on this german site: http://all-inkl.com/wichtig/anleitungen/programme/e-mail/speedport-w724v-hybrid/liste-der-sicheren-e-mail-server_399.html