Mailcheap Limitations

The integration’s authentication token gets invalidated upon logging in each time.
The generated authorization API token expires every 24 hours, or when you refresh the service admin area while you are logged in.

WP Email Manager will periodically generate the API token, but when you refresh the service admin area, the token gets invalidated. This may result to unexpected results.

Potential Fix: Have a separate or dedicated admin user assigned to WP Email Manager.
Overselling is only supported in the Enterprise Cloud and Enterprise Dedicated Plans.

Overselling is a term used when a hosting provider sells more bandwidth and disk space than they physically have. Most websites will not use all the resources allocated by their provider, leaving the provider with leftover bandwidth and space each month. Providers sometimes take a risk by selling the leftover space to other customers to maximize profits.

An example of this Mailcheap limitation (if you are using the Enterprise Shared plan) is where if you have subscribed to a 20Gb plan, and your client creates an email account with a disk space of 10Gb, the next client will be limited to 10Gb.

For other providers, irrespective of the subscription plan, you can set a higher limit, as long as the actual total disk space used by all the email accounts doesn’t surpass the subscription plan’s limit.

Learn more about overselling here.