gmail send as adress (another smtp-server)

If have configured my gmail account in eMClient. In GMail Web Client i have configured to use another smtp Server (GMX) to send by mails (send mail as function on accounts and Import in setting).

I have tryed to change the smtp Server in the eMClient to the GMX smtp Server, but this does not work.
I have configured a second account for the GMX Mail. Now i can send the mails with GMX smtp but outgoing mails are not stored in the GMail account. I have not found to configure this.

simply set an Alias in the account settings - the messages should be sent through the correct smtp server then.

Thanks for response. I think it now works as expected.