Is there a service/system for corporate mail?

Question

Email

Please tell me the mail system/service, in which:
1. All letters would come to one common mailbox (such as [email protected]);
2. Each employee of the company would have its own account, from which it is possible to respond to these letters in this general mailbox;
3. Emails have tags/labels. It is desirable that the system automatically assigns (by filters?)
4. Layout of letters to employees' personal folders (desirable). This is so that if the letter is in the "Vasya" folder, then Vasya is in charge of this letter / correspondence.
5. So that letters are combined into chains.
We tried Gmail (G Suite), but each employee has his own mailbox, there is no single one. They made a group like "joint inbox", but this way you can only receive letters - you can't answer, some kind of nonsense. They delegated the mailbox of one employee to another, but then all employees will have the same signature in the letters, i.e. personal signatures are not provided for delegation. There are no words. And there are no more options either - tell me, please.

Answer 1

try Megaplan

Answer 2

i dont know what to say
let them come :)
then each employee should have their own account + info account. imap is needed here
if the sending party affixes these tags, then on Unix this is done by the mail server (sendmail, postfix, exim + procmail)
conflicts with item 2 or you have not described in detail. the folder "Vasya" and the account "Vasya" are different
this is already a client program should be able to

Answer 3

No problem. Set up an IMAP4 server, make shared folders for a shared mailbox via public namespace, and easily work with them from user boxes. Any client.