Following is the response from the server space provider, I have got upon requesting 1GB mail box size for each e-mail id for the website hosted in shared environment.Please note that in the normal shared hosting environment, you will be  facing the following issues if you are allocated with more email  space:Generally domains that have more number of Email id's and email space have lot of mails stacked in the server which creates spike in  inode creation in the server . This in turn creates file system errors  affecting the disk integrity.Note that since you are in a shared hosting environment , the CPU usage per domain is 12 to 15 % only. If lot of mails is stacked in the  server, the mail server CPU usage for your domain will go high and it  will affect the performance of the entire serverHence in order to maintain the highest level of performance on our  shared servers, we are limiting the mail box maximum size to 100MB  only.Questions:How appropriate are these technical reasons?Is there any way they can provide 1GB mail box and simultaneously keep constraints or check on other factors and avoid above mentioned problems?
Are these technical reasons correct for not providing 1GB mailbox for each e-mail ID on shared hosting environment?
email;shared hosting
Sounds like you've exceeded your shared hosting capabilities. Your hosting provider uses hosted services to keep the costs down for everyone. Therefore they have to put resource limits on each account so that the resources are shared out equitably among all the accounts on the shared server. It's their server, and their ballcourt, so it doesn't matter what we think they can do, but how they plan to run their system for best response for the rest of their users on the server.You have two options:See if they have a higher service level that lets you do what you want.The usual way of handling this is to move your email services to another system. Getting an email service provider that will provide you with 50GB of space per user also can get you on a system that has far better delivery of email, is not so likely to get blacklisted when one bad customer on the hosted server decides to spam everyone. $2.00 a month for each email account was a really good move for us because it allowed our company to send more email, receive larger attachments, and know that PSF, DKIM, DomainKeys records were processed to allow for a massive reduction in the bounce rate we were experiencing from having the email hosted through the shared server account we were using at the time.To put it another way, the advantages of getting services that do what you need will pay off better than attempting to argue a service provider into doing something they haven't engineered the system to do.