Mapping Local Users with SMTP remote server Users !

[moazrefat]

i have been search for long time how to map local users to use a remote smtp and i hope that you can help me to do this task ,
for example , i have users locally on zentyal server called moaz.refat and the same name on remote smtp server and every local user on the system have the same property .

so for example i need moaz.refat which is locally registered to authenticate and send emails through the remote server which also has this username

zentyal offers to retrieve emails from remote pop3 pop3s imap and imap3s , but i don't know how to do authenticate trough the remote SMTP server

can anyone help in this trick ,   

thank you in advance.

[christian]

easy: do not use Zentyal SMTP and configure remote SMTP server at mail client level 

[moazrefat]

this is might be a solution but not all of use is using email clients , some of users depending on webmail , but this is not a solution

i just need to know if there is a service live mail retrieval service which is in user corner, or any another way to do ,

as per your solution users users must have remote smtp servers username and password and this is not true , they will only have the local user password as i intend to stop users from checking their emails from the internal network & over vpn connection only ,

do you understand me ?

thanks christian for you reply .

[christian]

No I don't understand you.
You ask how user could use remote smtp server using remote account and then say "but they don't all have remote account".

I first was surprised to know why you were asking such question but refrained myself to ask.

Maybe either me or you don't understand how mail works 
Why, using webmail, would you need to rely on remote SMTP server?

[moazrefat]

no i understand well email service , but see this Scenario
i'm system administrator , and we have a remote email service pop3,imap and smtp and i created on the remote server a user name identically to the local users to disallow users from accessing their mails outside of our network so he is forced to connect through out VPN service to get their emails with his local user who can fetch&send emails from&through the remote service, you might ask me a question why don't create you own email services ?
because if the email server that i created is down for any reason like electricity failure no one from the public will be able to send us emails , that is not important to this ,

in brief i want to configure every local user to fetch and send emails, now i already can use the email retrieval service,
do you know what i mean exactly , in gmail you can configure your email to "fetch emails from" & "send emails as" !!
is it clear now ?

thanks for your cooperation and support christian & i hope everyone can help to support .

[christian]

"send mail as" has nothing to do (almost) with use of external SMTP server.

I'm using one single MTA (my local Znetyal server) with 4 different mail addresses. This MTA is configured to receive only one mail address, the three others are fetched from external mail servers, and I don't have any need to use external SMTP server, even using webmail (Roundcube is able to manage multiple identities). In case I want, for some reason, to use external MTA, I just configure my mail client to use it. No change at Zentyal level (except capability to access external SMTP protocol from LAN)