Sites that have more emails created or use more disk space for emails or more traffic used for mails mean
1. The website is using mail server extensively
2. Have more email ids created mean that the client is either a mid size or a big corporate
3. Mail server is being used for mass mailing
Websites that use mail servers extensively use high cpu and memory. This is because the client might be accessing the mail server frequently or number of emails in the website mean, more sessions to the mail server from a single domain itself. This means others in the server will have fewer connections available for accessing the mail server. Such high users of mail servers are usually medium or big size corporate. Such clients would require a very high quality service and uptime.
Such clients will stay with you longer, provided you suggest them the right solution at reasonable cost. Instead of stacking them as one among your shared hosting customer it is good to take this up with the client, he might upgrade to a higher account. The amount of sessions and resources allowed per domain in a corporate mail server or semi dedicated server is high when compared to a shared reseller server. Hence such an upgrade will enchance the mail server performance for your client and you can also retain the client with you.
If the mail server usage is high due to mass mailing, then it is better to remove such accounts as they affect the server performance and also affect mailing opreations and delivery for other websites in the server. Mass mailing or bulk mailing is strictly prohibited in shared hosting servers and hence must not be hosted in your reseller account.
In case of any clarification required for choosing the correct package for upgrade, please contact support by creating a ticket.
