Tanmaya,
I am really interested in knowing how that works. Let me see if I understand it right. Jodohost runs more than one mail server. At the time of creating the reseller account it becomes assigned to one of them. From that point on all messages sent to, or from, email accounts on reseller's or his/her end-user's domains are processed by that mail server only. So, when this machine is down, for any reason, the messages destinated to accounts on that server are being held by the sending mail server until the time-out. If the time for making delivery attempts by the sending mail server is shorter than a down-time of destination server, the messages are being bounced back with note "undeliverable".
In case of making mail relay enable, all reseller's and his/her end-user's domains DNS zone file receive additional MX record with the address of secondary mail server (another one run by jodohost) with the value higher then the MX record for the primary mail server. If I remember right the theory of DNS - the mail server with the lowest number in MX record is the one actually hosting mail accounts, those with higher number are "buffering".
BTW, I remember snooping around big hosting providers DNS zone files and seeing that XO communications used four mail servers, Covad - six. Their DNS server no longer allow listing all records, but if you run "nslookup xo.com" it will return four ip addresses.
So, how many mail servers does jodohost run? "nslookup mail.mysphere.biz" returns only one ip address. That leads me to the question: does it make sense to enable mail server if you have only one? Or perhaps I have to specify the mail server of third party company? But then, how does that secondary mail server know that it is supposed to cache messages destinated to mailbox on jodohost mail server?
Can someone shed some light on this? Explain in lame terms? I don't have to emphasize the importance of mail server. All my clients don't mind their site being down, even for hours, but when they can't log into their mailbox I am getting a phone call right then. It would be nice to be able to say: yes, the server is down but all messages are being collected/buffered, you will get them as soon as the server is up again.