Which email client to choose for iOS?

Question

iOS

Task:
- Process correctly mail from google, mail, yahu and iCloud services, as well as corporate
- IMAP support
- Separate signature for each email address
- Work with filters and folders / subfolders
- Pulling up the address book (not phone)
- Search for a word / addresses among all letters at once and / or in a separate account
- Send letters with attachments (dropbox, iCloud)
- Availability of a calendar (as it is in Boxer)
Immediately exclude clients from MailRu (their native and myMail), Spark, Boxer, gMail, Mailbox and Yahoo. I used all this, there were crooked places everywhere.
Now I've settled on CloudMagic, but it's also frustrating. The address book reads only the phone book. The mail address can only be loaded if I have previously sent a letter from the client to this address. Sent letters are copied to its own sent folder, and not to the general one, which is on the server. The search for a particular letter is something very long, and not always successful.

Answer 1

Maybe Thunderbird?

Answer 2

The next question is "Which hand is right to eat?".

Answer 3

By far Spark by Readdle is by far the best email client for iOS and Apple Watch and for some reason it's free.
It can do everything and even more, I have been using it for more than six months.

Answer 4

Perhaps there is something I don't know. But all of the above except the calendar is able to standard client.