Mail plans come in sizes — five, ten, twenty-five — and the obvious move when the fifth mailbox is taken is to buy the plan above it. You do not need to: mailboxes can be added to the plan you already have.
How to add one
Open the mail service in the client area. Alongside it you will find the option to add mailbox capacity, one at a time, as many as you need.
It appears on your next invoice as a separate line beside the plan, on the same billing cycle, and prorated for the part of the month that has already passed.
What happens on the server
The limit on your plan is recalculated immediately: five plus one is six, and the sixth mailbox can be created straight away. Nothing is migrated and no existing mailbox is touched.
The same works in reverse. Cancel the add-on and the limit returns to the plan's own number — but only if you are under it, so delete the mailbox first.
When the bigger plan is cheaper
Add-ons are priced per mailbox, and plans get cheaper per mailbox as they get larger. There is a point where moving up costs less than adding more.
The rule of thumb: a few extra mailboxes, add them. Half a plan's worth, ask us — we will work out which is actually cheaper for you rather than selling you the larger number.