Contacts and distribution lists

On-premises Exchange

This page covers hosted on-premises Exchange, not Exchange Online.

Contacts

A contact is an address-book entry for someone outside the organization. It has no mailbox and consumes no mailbox quota — it exists so people appear in the address book and can be added to distribution lists.

Each contact has general settings (name and external address) and a mail flow tab for delivery options.

Use contacts for suppliers, partners and contractors who need to be findable in the address book but who receive mail somewhere else entirely.

Distribution lists

A distribution list delivers mail addressed to one address to every member.

Tab	What it controls
General settings	Name, address and membership
Addresses	Additional addresses that reach the list
Mail Flow	Delivery restrictions and forwarding
Permissions	Who may send to the list, and who manages it
Member Of	Other lists this list belongs to

A Report view lists the distribution lists in the organization with their membership, which is the quickest way to audit who is on what.

Restricting who can send

By default a list may accept mail from anyone, including outside the organization.

An unrestricted all-staff list is a standing risk

Anyone on the internet who learns the address can mail everyone in the organization at once. That is a phishing delivery mechanism and an accidental reply-all storm waiting to happen.

Restrict large or all-staff lists to authenticated internal senders, and use the permissions tab to say who may send. It is a two-minute change that prevents a bad afternoon.

Nested lists

A list can contain another list. This is useful — a department list inside an all-staff list — but nest sparingly. Membership becomes hard to reason about quickly, and loops between lists cause mail to circulate.

Dynamic distribution lists

A dynamic distribution list has no fixed membership. Its recipients are worked out each time mail is sent, from a filter you define — everyone in a department, everyone at a location.

The advantage is that membership never goes stale: a new starter matching the filter is included automatically, and a leaver drops out.

Its tabs cover delivery management, message approval, email options, MailTips and group delegation.

You cannot see the membership list before you send

Because it is evaluated at send time, there is no roster to check. A filter that is broader than you intended is discovered when the mail has already gone.

Verify the filter against the current directory before using a dynamic list for anything sensitive or wide-reaching, and prefer a static list where the audience must be exact.

Which to use

Use a static list when	Use a dynamic list when
Membership must be exact and auditable	Membership follows a directory attribute
The group does not map to any attribute	The group is large and changes often
You need to see who is on it	Keeping it current by hand is the real cost

Both depend on directory attributes being correct. A dynamic list filtered on department is only as good as the department field on each user.

Related

• Exchange mailboxes
• Transport and journaling rules

The tabs on each recipient type

Contacts carry Contact Settings and Contact Mail Flow. Distribution lists carry more, because they have membership and delivery behaviour of their own:

Tab	What it controls
Distribution List Settings	Name, alias and general configuration
Distribution List E-mail Addresses	The addresses it answers to
Distribution List Mailflow	Delivery restrictions and moderation
Distribution List Member Of	Other lists this one belongs to
Distribution List Permissions	Who may manage or send as the list

Dynamic distribution lists have no fixed membership, so instead of a members tab they offer All Members — a resolved view of who currently matches the rule.

A dynamic list's membership is resolved at send time

All Members shows who matches now. The list a message actually reaches is resolved when it is sent, so a user created or changed in between is included or excluded without anyone editing the list.

That is the point of a dynamic list, and it is also why a message can reach someone nobody remembers adding.

Reports for both live alongside: Distribution Lists Report, and the Empty Distribution Lists Report family in the mail templates.

Mail-enabled security groups

A mail-enabled security group is both a security principal and a mail recipient — it grants access and receives mail. Exchange Online exposes an Exchange Online Mail-Enabled Security Groups Report for auditing them.

Adding someone to the group grants them access as well as mail

Because the group does both jobs, adding a member for the mailing list also gives them whatever resource permissions the group carries. There is no way to take only the mail half.

Check what the group grants before adding anyone to it for mail reasons.