Guidelines on Sending Emails to a Large Number of External Users

by Raymond Poon

At times, most departments may have genuine needs of sending email to a large number of external recipients, and yet quite a number of such email was either bounced as undelivered email or returned with undeliverable notifications by the recipients' email servers due to the following reasons:

  • Departments' email recipient lists were outdated (e.g. the recipients' email addresses are invalid)
  • The size of the email attachment was too large, resulting in the email being rejected by the email servers at the recipients' end.

Sometimes the number of such bounced email or undeliverable email notifications was so huge (as the email is often delivered at the same time) that it jammed our email servers, causing prolonged sluggish email delivery. Worse still, complaints were received to ask the CityU to stop sending the email for reasons such as the recipients considered it as spam mail, or the email attachment caused the recipients' email disk quota severely depleted, resulting in their subsequent incoming email being missed.

As such, departments have to exercise care when sending email to a great number of external recipients. Moreover, it can also devastatingly damage the image and the operation of the University if this kind of email is sent without prior consent of the recipients. For example, if some recipients do make complaints to those Real Time Spam Black Lists (RBL) sites and have the university email server being successfully blacklisted, no CityU users will be able to send email to all those organizations that are using the RBL as a means to fight spam mail. Besides, it is also undesirable to send unsolicited email with an attachment as the recipients may not know who you are and whether your attachment is safe to open. If however you do have to send an unsolicited email with an attachment, please limit the size of the attachment to a minimum as the acceptable size limit of an email message for many email systems is well below 5MB.

In order to safeguard the reputation of the University, it is advisable to adopt the following guidelines for good practice:

  • No matter how small the number of recipients is, avoid sending commercial advertising material without their prior consent.
  • Avoid sending email to a large number of recipients without their prior consent and always keep an updated mailing list. Make a plan beforehand to obtain their prior consent and collect their email addresses, say, during an activity or while they visit our campus or your departmental website.
  • If sending unsolicited email is unavoidable, and in doing so without subjecting the University to any possible legal liability or ill-publicity, include a means in the email either to invite the recipient to join your mailing list or allow recipients to remove their email addresses from your mailing list (e.g. through clicking an URL). These removal requests should be dealt with in a timely manner. In general, an opt-in approach is preferred to an opt-out.
  • Avoid attaching any file in mass mailings especially with the unsolicited email (e.g. putting the file on the web site for downloading can be an alternative).
  • If direct attachment is unavoidable, keep it small by selecting the most appropriate way (e.g. for image file, keep the resolution to a reasonable level) and format (e.g. produce an electronic document in pdf format instead of image format) to generate the attachment file. Do not attach any file that has embedded scripts, macros or requires any software (including those plug-ins for browser) to execute as it may impose unnecessary security risks to the recipients and will likely be removed by the email server at the recipients' end.

Please watch out for the following upcoming laws related to the spam email and make timely changes to the respective business operations:

Anti-spam (Proposal)

Should technical assistance or advice be needed, please call our CSC Help Desk at 2788 7658.