Mailbox Storage and Pooled Quotas Explained

Your TrekMail plan comes with a pooled storage allocation. Email uses it on every plan. When your account has Drive access, Drive files use that same pool too. Starter, Pro, and Agency include Drive; Nano needs a Drive add-on or trial. A mailbox with a dedicated allocation uses the amount reserved for that mailbox instead. This guide explains the difference, what counts against each limit, and what to do when space runs low.

Who this is for

• Admins receiving "Storage Full" alerts.
• Users wondering why a mailbox stopped accepting new mail.
• Anyone trying to plan capacity around email + Drive together.

What counts against your pool

The pool is shared by everything that stores bytes on TrekMail:

• Email: every message in every mailbox: Inbox, Sent, Drafts, Spam, Trash, custom folders, attachments.
• Webmail Drive: files uploaded by mailbox owners through the webmail interface.
• Account Drive: files uploaded by the account owner through the dashboard, including any folder shared with the whole account.
• Trashed items: files deleted from Drive stay in Drive Trash for 30 days and continue to count against the pool until you empty Trash or those 30 days expire.

For a mailbox using shared storage, there is no separate "email-only" or "drive-only" partition. A small inbox and a large Drive, or the reverse, both use the same account pool.

Storage Limits by Plan

The full plan allocation is shared across all mailboxes and aliases by default. When Drive is available, Drive files use that allocation too. Enforcement is at the account level, not per mailbox, so one mailbox can use most of the pool while others stay small.

Expanding the pool

Two paid add-ons can extend your pool. Both add to the same single pool. There is no "mail-only" or "drive-only" capacity that competes.

• Dedicated Mail Storage add-on: purchased on the Billing page. Adds raw megabytes to your pool. Useful if you need more email/Drive capacity without changing your mail plan tier.
• Drive Add-on subscription: purchased on the Plans page. A separate subscription that adds anywhere from 250 GB to 100 TB on top of your pool, billed monthly or yearly in 10 currencies. See Drive Add-on Pricing & Plans.

The capacity available to mailboxes that use shared storage is calculated as:

pool = base plan storage
     + Dedicated Mail Storage add-on (if any)
     + Drive Add-on storage (if any)
     − any dedicated per-mailbox allocations

Read the full breakdown with worked examples in Pooled Storage Quotas Explained.

Shared vs Dedicated Mailbox Storage

Each mailbox can be assigned to one of two storage modes:

• Shared (default), the mailbox draws from the account pool together with every other shared mailbox. Best for teams where one heavy user is balanced out by lighter ones.
• Dedicated: a fixed amount is reserved just for this mailbox. The mailbox cannot exceed it, and other mailboxes cannot use it. Best for VIP accounts, executives, or any mailbox that needs guaranteed headroom.

The webmail header shows which mode is active, for example 0 MB of 5 GB (dedicated) for a dedicated mailbox or 0 MB of 50 GB (shared) for a shared one.

You can choose the mode at creation time (in all four mailbox-creation flows) and switch any mailbox between the two modes at any time:

1. Open the Mailboxes page.
2. Click the 3-dots menu next to the mailbox.
3. Choose Edit storage.
4. Tick or untick Shared Storage, set the size, and save.

Dedicated allocations are validated against the live pool when you save. If the allocation no longer fits, for example because another mailbox grew its dedicated allocation first, the system shows how much room is available. A dedicated mailbox uses its own allocation for both its mail and its personal Drive files.

How email storage is stored

Two background optimisations reduce the on-disk footprint of email behind the scenes, both are transparent and require no action:

1. Automatic compression. New mail is written with gzip compression. For typical text-heavy inboxes this trims ~20–30% off the raw size. Large binary attachments (images, PDFs, archives) are already compressed by their format and do not benefit further.
2. Attachment offload. Message parts larger than 512 KB are moved to cloud object storage and replaced with a reference inside the message. Your email client sees the message exactly as sent, attachments download on demand. Identical attachments sent to multiple mailboxes in your account are stored only once.

The usage number shown in the dashboard already reflects these optimisations. It is what is actually counted against your quota. Drive files are stored separately from email but contribute to the same pool number.

Checking usage

1. Global. The Overview page shows a progress bar of total account usage vs. your plan limit. The bar combines email and Drive into a single percentage.
2. Top Mailboxes widget. Highlights the mailboxes using the most email space.
3. Per mailbox. The Mailboxes list shows each mailbox's used storage (email only) in MB. Click the Storage column header or use Sort by → Storage (High to Low) to find heavy users quickly.
4. Drive usage. Open Drive (/drive) to see folder-level breakdowns of file storage in your account.

IMAP clients can also read the email quota directly via the standard GETQUOTAROOT command, most clients render this as a storage bar in the folder list. (IMAP only sees the email portion of the pool.)

Enforcement details

• Aliases share storage. An alias is an extra address that delivers into an existing mailbox; it has no separate storage. Mail addressed to an alias counts against its parent mailbox's, and the account's, pool. Adding aliases never grows your storage consumption.
• Drive files count fully. A 1 GB file uploaded to Account Drive uses 1 GB of pool, the same as 1 GB of email would.
• Drive Trash counts. Trashed files continue to count for 30 days. If you need bytes back immediately, empty Drive Trash from the Trash view.
• Grace margin (email). 10% above the limit is allowed for the last incoming message, so a single near-boundary delivery never bounces purely on timing.
• Max single message. 50 MB per email, including attachments. (For attachments larger than 18 MB, webmail auto-routes them through Drive as a download link instead, see Sending Large Attachments via Drive.)
• Enforcement point. Inbound mail delivery for email; upload checks for Drive. Reads (IMAP fetch, Drive download) are never blocked even when full.

What happens when you are full

If the account exceeds its total storage:

1. Incoming mail is rejected with 552 5.2.2 Mailbox is full. The sender receives a bounce notification.
2. Outgoing mail still works, though saving to Sent Items may fail if the send produces a copy that no longer fits.
3. Drive uploads are rejected with a "not enough space" error. Existing Drive files keep working, downloads, share links, opening them, only new uploads are blocked.
4. IMAP access is always available. You can log in and read or delete existing messages to free space.

Keeping one mailbox from filling the pool

Because the pool is shared, a single person treating Drive as personal cloud storage spends the allowance the rest of the account needs for mail. There are two ways to bound that.

Per-mailbox storage: give a mailbox a dedicated allocation, as described under Shared vs Dedicated Mailbox Storage above. That caps the combined mail and personal-Drive usage for that mailbox.

Per-mailbox Drive access: on the mailbox's Limits tab, reduce Drive to email attachments only, or switch it off. Email keeps working, including sending files over the attachment limit as a download link, but there is no file store to fill. This is the one to use when you are selling mail rather than storage, and it can be applied to many mailboxes at once.

Neither option deletes anything that is already stored; the Limits tab shows what a mailbox is holding and offers to remove it. See Limiting or Turning Off Drive for a Mailbox.

What happens when you downgrade or cancel an add-on

If you move to a plan with a lower limit, or your Drive Add-on is canceled, but your usage is already above the new pool:

1. Nothing is deleted immediately. All existing mail and Drive files are preserved.
2. New incoming mail is bounced until you free space below the new limit.
3. New Drive uploads are blocked with the same "not enough space" error.
4. You can still access everything via IMAP, webmail, or Drive to clean up.
5. Upgrading or reactivating at any time restores full delivery and uploads immediately.

For Drive Add-on cancellation specifically, there is a 7-day read-only grace period after the cancellation takes effect during which you can reactivate at the same tier before over-quota cleanup runs. If the account remains over its remaining cap after those 7 days, Drive files may be permanently deleted. See Canceling Drive Add-on.

How to free up space

In rough order of how easy and reversible each is:

1. Empty Drive Trash if you use Drive. Anything you've deleted in the last 30 days that you don't actually need.
2. Empty Trash and Spam in your mailboxes. Both count against the quota.
3. Delete large attachments. Sort by size in your client (Outlook, Apple Mail, Thunderbird) and remove heavy files you no longer need.
4. Delete large Drive files. Open Drive, sort folders by size, remove what you don't need.
5. Convert dedicated mailboxes back to shared. A dedicated mailbox locked at 20 GB but only using 2 GB is reserving 18 GB the rest of the account can't touch. Switching it to shared returns those bytes to the pool.
6. Buy or expand the Drive Add-on for headline capacity bumps (250 GB to 100 TB).
7. Upgrade the plan for a moderate bump (e.g. Pro → Agency adds 150 GB to the pool).

Related guides

• Pooled Storage Quotas Explained, full pool calculation with worked examples.
• Drive Add-on Pricing & Plans, the slider, tiers, and currencies.
• Trash and File Restoration, Drive Trash mechanics and 30-day retention.
• What is TrekMail Drive?, overview of the file-storage product.