Outlook Zip & Send ENT

Administrator Guide — deploying the Outlook add-in that packs the attachments of a message into one .zip, inside Outlook.

Audience: IT / Microsoft 365 administrators · Applies to: Slim Archiver Enterprise.

What the add-in does

Slim Archiver Zip & Send is an Outlook add-in. When it is deployed to a user, a Consolidate with Slim Archiver button appears in a Slim Archiver group on the ribbon while the user writes a message. The button opens the Zip & Send task pane, which packs the message's attachments into a single .zip, attaches it, and removes the original attachments. Everything happens inside Outlook: the Slim Archiver desktop app is not needed, and the attachments are not sent to Slim Archiver.

1. Requirements

Item	Requirement
License	Slim Archiver Enterprise. The add-in's manifest file is made for your organization's email domains and supplied with your Enterprise license (section 4); if you do not have it, contact support@slimarchiver.com.
Mail server	Exchange Online (Microsoft 365). The add-in requires the Outlook add-in API set Mailbox 1.8; on-premises Exchange Server (2016, 2019, Subscription Edition) supports only up to 1.5, so the add-in does not load for on-premises mailboxes.
Outlook	Outlook on the web; the new Outlook for Windows; classic Outlook for Windows with Microsoft 365 (Version 1910 or later) or Outlook 2021 and later; Outlook for Mac. Not the Outlook mobile apps: they support only up to Mailbox 1.5, and the add-in has no mobile layout.
Network	Outlook must reach https://outlook.slimarchiver.com (the add-in's page, script and icons) and https://appsforoffice.microsoft.com (Microsoft's Office add-in library). Its fonts are part of the add-in.
Permission	Read/write item (ReadWriteItem): the add-in can read and change the message being written, which it needs to read the attachments, add the archive and remove the originals. It does not request access to the whole mailbox (ReadWriteMailbox).

2. Deploying the add-in

Deploy the add-in centrally from the Microsoft 365 admin center. The steps follow Microsoft's instructions for a custom add-in; Microsoft may rename the menu items.

1. Sign in to the Microsoft 365 admin center as an administrator who may deploy add-ins (for example an Exchange Administrator or a Global Administrator).
2. Go to Settings → Integrated apps, open Add-ins and select Deploy Add-in.
3. Choose to upload a custom add-in, select the option to upload the manifest file, choose the manifest file supplied with your license, and select Upload.
4. Choose who gets it: Just me (to try it first), Specific users/groups, or Everyone. Microsoft recommends assigning groups. Only these users get the button; this is how access is controlled (see section 4).
5. Select Deploy. Users may need to restart Outlook; Microsoft states that a deployed add-in can take 24-72 hours to appear.

2.1 Updates and removal

• The add-in's page and code are loaded from outlook.slimarchiver.com each time the task pane opens, so changes to them reach users without a new deployment. The manifest (the button, its text and the permission) changes only when you upload a new manifest: select the add-in in the admin center and choose Update. Upload a new manifest also when your license is renewed or a domain is added (section 4).
• To withdraw the add-in, remove it, or remove users or groups from its assignment, in the admin center; the button then disappears from Outlook for those users (this can also take time).

3. What users see

1. While writing a message, the user selects Consolidate with Slim Archiver on the ribbon (group Slim Archiver). In Outlook on the web and the new Outlook, add-in buttons can also be under Apps. The Zip & Send task pane opens.
2. Email Attachments lists the attachments that will go into the archive, with their sizes. The list updates when attachments are added or removed; on clients that do not report changes, the ⟳ button reads it again.
3. Archive Filename is attachments.zip by default; .zip is added if the name does not end with it.
4. Consolidate Attachments runs the steps shown in the progress bar and the Activity Log: reading the attachments, compressing into .zip, attaching the archive, verifying that it is attached, removing the originals. The log ends with Attached <name> and replaced N original(s).
5. The ☀ / ☾ button switches the task pane between dark and light; the choice is remembered by that Outlook, otherwise the system theme is followed.

3.1 What goes into the archive

Attachment	In the archive	Notes
Files attached to the message	yes	Each keeps its file name inside the archive.
Pictures placed in the message body (inline)	no	Left as they are.
Attached Outlook items, and cloud attachments (links to OneDrive or SharePoint files)	no	Left as they are. The log says N attachment(s) skipped (inline or non-file) — they will be left untouched.

3.2 Limits

• 25 MB in total. The included attachments may add up to at most 25 MB; above that the add-in stops before it changes anything. Microsoft also limits an attachment added by an add-in to 25 MB, so if the archive itself ends up larger (attachments that do not compress), Outlook refuses it and the originals stay.
• Unique names. Two attachments with the same file name cannot both go into the archive: the run stops with File already exists and nothing is changed. Rename or remove one of them and try again.
• A standard, unencrypted .zip. The archive uses standard ZIP (Deflate) compression and opens with any ZIP tool, including Windows File Explorer. It is not a .slim archive and it is not encrypted; for confidential content, use an encrypted archive from the desktop app instead.

4. Access and licensing

The manifest supplied with your license carries a signed license for your organization's email domains and, if your license has an end date, that date. Each time the task pane opens, the add-in checks it inside Outlook (nothing is sent to Slim Archiver):

• it works only for users whose email address is in one of those domains or a subdomain of one (a license for contoso.com also covers uk.contoso.com);
• it stops working after the license's end date;
• a manifest without a valid license, or a changed one, does not work.

When the check fails, the task pane shows Enterprise Feature with a line that says why (section 6). For another email domain, or after renewing a license with an end date, ask support@slimarchiver.com for a new manifest and upload it (section 2.1). Deploy the add-in to the users and groups covered by your license. Opened outside Outlook (for example in a web browser), the add-in's page shows Enterprise Feature and does nothing.

5. Data and security

• Attachments stay in Outlook. They are read, compressed and attached again inside Outlook, in the add-in's task pane. The add-in sends their content nowhere, neither to Slim Archiver nor to any other service; it makes no network requests of its own, and its license check (section 4) also runs inside Outlook.
• What is loaded from the network: the task pane page, its script, the ZIP library and the icons from outlook.slimarchiver.com (hosted on Cloudflare Pages), with its fonts; Microsoft's Office add-in library from appsforoffice.microsoft.com. See the Privacy Policy on slimarchiver.com, section 3.
• Originals are removed last. The archive is attached and confirmed first; only then are the originals removed. If any step fails, the log says Your original attachments were NOT removed.
• Attachment names are shown as plain text, never interpreted as HTML, so a crafted file name (for example in a forwarded message) cannot run code in the task pane.
• Slim Archiver policy does not apply. The add-in does not use policy.json, the DLP rules or SSO enforcement, and it writes nothing to the Slim Archiver audit log. Messages are governed by your mail system's own controls; after consolidation they see one .zip attachment instead of the separate files, so check that your mail data-loss rules inspect the contents of .zip attachments.

6. Troubleshooting

Message or symptom	Meaning & fix
The button does not appear	The add-in is not yet deployed to that user (allow up to 72 hours and restart Outlook), the mailbox is on on-premises Exchange, the Outlook version does not support Mailbox 1.8, or it is a mobile app (section 1). In Outlook on the web and the new Outlook, also look under Apps.
This add-in was deployed without a license. ...	The deployed manifest is not the one supplied with your license (for example a copy without its license). Upload the supplied manifest (section 2.1).
The add-in's license does not cover <domain>.	The user's email domain is not in the license. Ask support for a manifest that includes it.
The add-in's license expired on <date>.	The license has ended. After renewal, upload the new manifest.
The add-in's license is not valid.	The manifest was changed or damaged. Upload the original file again.
This version of Outlook cannot check the add-in's license.	Update Outlook (section 1).
The pane shows Enterprise Feature inside Outlook without any of these lines	Microsoft's Office add-in library did not load. Check that appsforoffice.microsoft.com is reachable (section 1), then open the pane again.
No consolidatable attachments found on this email.	The message has no file attachments; inline pictures, attached items and cloud attachments do not count (section 3.1).
Live attachment updates unavailable on this client — use Refresh.	This Outlook does not report attachment changes to add-ins. After adding or removing attachments, select ⟳.
Consolidation aborted: Combined attachments exceed the 25 MB in-add-in limit.	The attachments add up to more than 25 MB (section 3.2). Send fewer or smaller files, or create the archive with the desktop app.
Consolidation aborted: File already exists	Two attachments have the same name. Rename or remove one and try again.
Consolidation aborted: Archive attach could not be verified — originals left untouched.	Outlook did not confirm the new attachment. Check the attachment list, remove a partial archive if one is shown, and try again.
Consolidation aborted: followed by another message	Outlook refused a step, for example an archive larger than 25 MB; the text is Outlook's own. Nothing was removed.
Could not remove <name>: ...	The archive is attached, but Outlook kept this original. Remove it by hand before sending.