Mass or bulk emailing using Office 365

Office 365 email has limits which can prevent use of the service for mass mailing but there are alternatives available, such as the University's mailing list system.

What are the limits  

Only 100 recipients can be added to each email (the email won't send if you have more recipients) , only 30 emails can be sent every minute (emails will be queued and gradually released if you try to send more) and you cannot send email to more than 10,000 recipients in one 24 hour period (you'll have to wait to send more messages once you reach this limit). We are not able to change these limits in Office 365. For more information, please click here. The e-mail limit can be increased to 500 by contacting the IT Service Desk.

When you contact the Service Desk, you should include a brief reason and if possible give some indication of how many recipients you will be sending to.

If you exceed the above rates, you will get a message saying that delivery has been delayed. The emails still waiting to be sent will be queued on the University mail servers and delivery will be retried periodically. Once your average send rate drops below the above limits, your emails will be sent. You will not need to resend the emails yourself.

Mailing List Service for non-personalised emails

The University provides a mailing list service which can allow you to create, manage and send a standard, non-personalised email to large numbers of users.  The membership of the mailing list can be updated simply by cutting and pasting lists of email addresses allowing you to send email to those recipients in a controlled and recorded way.  The mailing list service has a wide variety of features which includes allowing self-subscription, allow anyone to post to the list, requiring moderation or preventing sending to the list for all but specific individuals.  For more details on the mailing list service, and to obtain a downloadable application form to create a mailing list, please refer to

Using an IMAP profile in Outlook for personalised emails with mail merge

If you need to send out personalised email messages to large numbers of people, then you probably use mail merge.  If you need to send our more than 10,000 personalised emails then you will not be able to send via the Office 365 email service, but, it is possible to setup outlook to send email using the University of Leeds SMTP servers and avoid the Office 365 email limits. 

You will need to request an increased email send limit for the email address which you wish to send the messages from.  You may already have this in place if you have sent mass mails from this address before.  You will only need to make this request once.  To do so contact the IT Service Desk stating the email address you wish to use and the purpose for the mass mailing. You are limited to adding no more than 400 email addresses to each email to send when using the University of Leeds SMTP servers. If you need to send one email to more than 400 recipients you should use the mailing list service (see above).

Note : If you log in to your PC using an ADMIN account, you will need to use Outlook from within the Desktop Anywhere service.  All other staff can complete the following  instructions using their normal desktop as follows;

  • Go to Start > Control Panel > Mail (32bit) > Show profiles
  • Tick Prompt for a profile to be used then click Add
  • Profile Name : Mass mailing
  • OK

When prompted, setup an IMAP link to your account by selecting;

  • Manual setup > Next
  • Select POP or IMAP
  • Under "Your Name" choose a display name you would like the message to appear to come from
  • Under "Email address" enter the email address you wish to send the message from - this must be the address which has the increase send limit mentioned above.
  • Account Type: IMAP
  • Incoming mail server :
  • Outgoing mail server :
  • User Name : of the user account with the email address you are sending from
  • Password : *********

Under More Settings > Advanced

  • Incoming Server (IMAP)  :993 , Encryption : SSL
  • Outgoing server : 25 , Encryption: None
  • Now click OK and your Account Settings will be tested.

Once all tests complete successfully and you will have a new IMAP profile setup in Outlook. Each time you start Outlook you will be prompted to select a profile. In future, to carry out mass mailing;

  • Close and restart Outlook
  • Select the "Mass Mailing" profile.

When you have finished your mass mailing;

  • Close and restart Outlook
  • Select your "Default" profile.

University Mailing Lists

For more information about the mailing list service, including a list of all public lists, see:

A mailing list is just a list of email addresses. An email sent to the mailing list will be received by everyone on it. The University has its own mailing list system.

To apply for a new mailing list you'll need to print off and complete the application form and send it to the User Admin team (via the IT Service Desk).

Why are sending rate limits imposed?

We experienced several instances of lots of spam being sent from single University email accounts. This usually happened after a user's account was compromised.

Spam email is often sent to many recipients at once and can cause the sending site to be blacklisted by other mailing systems. This causes all mail from the University to be rejected by those systems. By limiting email sending rates, we can prevent too much spam leaving the University and reduce the risk of email from the University being blacklisted.