Sending as a Microsoft 365 Group

A Microsoft 365 Group, a distribution list or a mail-enabled security group has an email address of its own, and a member who has been granted Send As or Send on behalf on it can put that address in the From field. Sigil treats the group’s address as a mailbox like any other: switching the From field to it fetches the group’s signature, and the person who pressed Send can be named in it exactly as for a shared mailbox.

Nothing has to be set up in Sigil for this. The group needs no licence, no sign-in and no entry anywhere; the permission to send as it is granted in Microsoft 365, not here.

How to send as a group

The person switches the From field in Outlook, in a message started from their own mailbox. That is the whole gesture, and it is the one Sigil sees. A new message, a reply or a forward all work.

1. In Outlook, start a new message, a reply or a forward from your own mailbox.
2. Change the From field to the group’s address.

The add-in notices the change and applies the group’s signature, replacing the one already in the message.

For the group’s address to appear in that dropdown, an administrator grants the permission in the Microsoft 365 admin center or Exchange admin center, under the group’s settings. Microsoft’s guide is Allow members to send email as a group. Send As makes the message appear to come from the group alone; Send on behalf shows the recipient both names. Sigil signs both the same way.

The way that is not signed

Outlook on the web and the new Outlook also let a member open the group itself, under Groups in the folder pane, and write a message from inside it. That message is composed in the group’s own mailbox rather than the person’s, and Outlook does not run add-ins there at all. It is a rule of the platform for every add-in, not a limit of Sigil’s, and there is nothing to configure around it.

So a message written from inside the group’s space goes out with no signature, while the same message written in the person’s own mailbox with the From field switched to the group is signed. If people in your organisation write from the group’s space, the practical answer is to tell them to switch From instead. The result is the same message from the same address, and this one carries the signature.

What the signature contains

A group has a name and addresses, and not much else. It has no job title, department, phone numbers, postal address or manager, and no photo Sigil can reach. So when the group’s signature renders:

• {{displayName}} is the group’s name and {{email}} is the address the message is sent from, the group’s own or one of its aliases;
• every other mailbox placeholder is empty, and a conditional section around one closes, exactly as it does for a shared mailbox with no phone;
• the sender placeholders work unchanged. The person sending is never the group, so {{#onBehalfOf}} opens and {{sender.firstName}} names them. “Kind regards, Jane Doe on behalf of Sales” is what an ordinary template renders from a group, with nothing added;
• any profile field you have defined reaches the member who sent the message, through {{sender.custom.<key>}}. A group has nobody to fill in a profile of its own, so the plain {{custom.<key>}} form is empty for one unless an administrator has entered answers against the group’s address under Profile fields. If a group’s signature should carry the sender’s pronouns, the sender form is the placeholder to use.

Your existing template is therefore already right for a group in most cases. The one thing to look at is any line that assumes a person: a “Chat with me in Teams” link, say, which leads nowhere useful from a group’s address. Two ways to handle it. Put the line behind the notGroup condition, so it disappears for a group and stays for everyone else. In the designer, open the block’s Show when rules with Add rules…, choose a rule and pick “The mailbox is not a Microsoft 365 Group or distribution list”. In the HTML editor’s field list it is “Not sent from a group mailbox”. Or give groups their own template, below. Its twin, isGroup, is for a line only a team mailbox should carry. They became a pair before a condition could be turned round, and either still works; in the designer’s rules dialog, not on isGroup means the same as notGroup.

Giving groups their own template

Assignment rules can match on mailbox kind, which is user for a person, a shared mailbox or a resource mailbox, and group for a group’s mailbox. One rule with the value group sends every group in the organisation to a template of your choosing, and covers groups created next month without anybody touching Sigil. An email-address rule works too, for one group at a time.

You need access to assignment rules. Among the built-in roles that is Admin only; a custom role that includes assignment rules works too, as do a partner’s Owners, Admins and Technicians in an organisation they manage.

1. Open Rules in the portal sidebar.
2. Choose Add rule.
3. Enter a Rule name.
4. Under Match on, choose Directory attribute.
5. Under Attribute, choose Mailbox kind.
6. In Matching value(s), enter group.
7. Under New messages and under Replies, pick the template groups should get.
8. Choose Add rule.

The dialog reminds you that group matches the mailbox of a Microsoft 365 Group or distribution list and user matches everything else, shared mailboxes included. The rule is saved as soon as it is added. For one group at a time, choose Email as the attribute and enter the group’s address instead. See creating a rule.

Rules that match on an Entra group’s membership do not apply to a group’s own mailbox, because a group is not a member of anything a rule can name. Email and Email domain rules match a group exactly as they match a person. Every other attribute is empty for a group and so matches nothing, which means a group that no Mailbox kind, Email or Email domain rule catches gets your default template.

Where groups appear in the portal

Every box in the portal that names a mailbox accepts a group’s address, and the suggestions list offers groups alongside people, marked “Group mailbox”. Two boxes leave groups out of their suggestions: inviting a portal user, which a group cannot be, and excluding a mailbox in cost management, where the address has to be typed in full. The designer’s preview boxes suggest groups without the marker. You can preview a group’s signature, simulate the rules for it, send a test email as it and download its signature, all as for any other mailbox.

The preview’s second address box, “sent by”, shows what a colleague’s message from the group will say, including whether the on-behalf-of clause opens. See previewing a shared mailbox send.

Cost

Group mailboxes are free, alongside shared and resource mailboxes. A group holds no licence, so it is never a seat, and the colleague sending from it is already counted in their own right. See billing.

In cost management a group can be listed like any mailbox. In exclusion mode that saves nothing and only stops its signature, and the row says so; in inclusion mode a group nobody lists gets no signature, so the row says it is included for free.

If a group is not getting its signature

Check, in this order:

1. Was the message written in the person’s own mailbox with the From field switched? A message written from inside the group’s space is never signed, as above.
2. Is the group mail-enabled and visible? A group hidden from address lists cannot be sent as from Outlook for Windows at all; that is a Microsoft restriction on the Send As permission, and the message never reaches Sigil.
3. Does the person’s own signature apply? If not, the problem is not the group. Start with troubleshooting.
4. Has a group just been created or given a new alias? Sigil looks an address it has not seen before up in Microsoft 365 on its first send, so a new group is found as soon as Microsoft’s directory search lists it, which can lag briefly behind the group’s creation. A change to a group Sigil has already seen, such as a new name, can take up to a quarter of an hour to show in a preview. In a signature it follows every other directory change: up to an hour, and then one further compose.