GODT-966 Fixed CI issues (WIP)
WIP GODT-966 modified behavior of APPEND.
WIP GODT-966 implemented test for possible order of operations.
WIP GODT-966: code cleanup and refactoring.
WIP GODT-966 fix for linter.
Other: Minor refactoring.
- [x] write tests to check that IMAP and SMTP servers are closed when there
is no internet
- [x] always create new go-smtp instance during listenAndServe(int)