Mass Mailings

In general, Microsoft 365 is not designed to be used for mass mailings:

• Accounts for current UT users have a default limit of 700 recipients per hour.

• Shared or resource mailboxes (shared/room/equipment) are subject to Microsoft's default limits.

While we cannot provide detailed insight into the exact limitations Microsoft places on outbound senders, we can state that the number of recipients and total email volume sent within a given time are potential triggers. Microsoft's outbound spam filtering monitors and takes action on outbound senders in order to prevent compromised accounts from sending phishing or spam emails. 

If Microsoft's outbound spam detection is tripped, the sender is placed on a blocked senders list. Microsoft 365 admins are able to remove blocked senders from this list, but if a sender gets blocked too many times in a certain period of time, we must open a support ticket with Microsoft to have the sender unblocked.

If you plan on routinely sending bulk messages, you may want to look into a bulk email service. The University Development Office runs a service called Eloqua that may be appropriate for your mass mailing. Other alternatives are UT Lists or Group Email (Emma), depending on your use case.

If you are only sending to internal Microsoft 365 users, you can create an distribution group and add the intended recipients as members. Sending email to a distribution group provides a workaround to the recipient limits, as the group counts as only one recipient regardless of how many members it contains.

If you are going to be sending several hundred messages to several hundred recipients, we suggest that you break up your list into separate lists and send the messages throughout the day. If you do end up on the blocked senders list, reach out directly to postmaster@utexas.edu for assistance.

Shared Mailboxes - Individual vs. Resource

There are two distinct categories of Microsoft 365 mailbox:

Individual Mailboxes

Individual mailboxes are owned by and represent a specific person, and associated with that person’s EID. They are accessed by signing into Microsoft 365 with the person’s EID credentials and/oror M365 email address and EID password.

Shared or Resource Mailboxes

Shared or resource mailboxes are:

• Shared between a department, group, or role

• Usually accessed by being granted full access permission to the resource mailbox

• Can represent:

  • A department (e.g. UT Service Desk)

  • A project or program (e.g. Bevo Party Planning Committee)

  • A role (e.g. president@utexas.edu)

  • A resource (e.g. room, vehicle, or equipment reservation)

While individual mailboxes are automatically provisioned for most new employees, shared or resource mailboxes can only be created by existing resource mailbox owners, the Service Desk (upon request), as well as by most local desktop support via the Resource Admin Tool.

To have the Service Desk create a resource mailbox on your behalf, contact them with the following information:

• Desired display name and email address

• Names and EIDs of the users who will have access to the account

• Intended use of the mailbox (room reservations, shared calendar, shared mailbox, etc.)

• Any requests for advanced calendaring options (e.g. automatic acceptance of calendar invitations, extending booking horizon, allow or disallow conflicting meetings, etc.)

More About Automated Calendaring

Automated calendaring configuration settings are plentiful, although the controls are not entirely exposed to the end-user. In addition, different settings are available depending on the resource mailbox ‘type’ (shared, room, or equipment). More information on hidden calendaring options are available in Microsoft’s documentation, but these can only be configured via PowerShell.

For advanced calendaring configuration, contact the Service Desk and provide your resource mailbox address and a description of your desired configuration (or the address of a similarly functioning mailbox).