Many organisations have policies that state that it is unacceptable to send emails to large numbers of users either inside or outside the organisations if you don’t have the recipients’ consent. Mass emails present their own problems, especially with attachments. Here’s a quick run down as to why.


The general term for mass unsolicited emails is “spam”. The sorts of emails typically associated with spam are those for dodgy investments (“pump and dump” schemes), growth pills, religious messages, phishing attempts, viruses and everything in between. Many organisations have invested in anti-spam filtering technologies to reduce the amount of junk that they receive (see my previous posting relating to scam/phishing emails for some statistics). The technologies to identify spam is always a “best guess”, using a variety of techniques, which means that some spam gets through and some legitimate emails get blocked.

At a very basic level, there are two main methods for preventing spam. Firstly, there are blacklists where servers who are known to send spam are prevented from sending any emails whatsoever to the organisation protected by anti-spam filtering. Secondly, emails that are received from “clean” servers have their content assessed to see if it matches the profile of known spam. If the score from this assessment is higher than the threshold decided upon by the protected organisation, it won’t get through and, in many cases, the sender’s servers are automatically added to the blacklist (or “greylist“). Rules vary for different products, but may include:

  • Sending to a large number of people
  • BCC’ing instead of sending to explicit addresses
  • Not including a standard greeting (“Dear Sue,” for example)
  • Having a reply-to set differently to the sender’s address

Organisation impact

A key point is that black-and greylists are shared and so if an organisation gets blacklisted it won’t be able to communicate with any organisation using that black- or greylist. Members of an organisation can, quite unwittingly, get their organisation blacklisted, thereby causing a lot of inconvenience to their colleagues.

Which is why organisations take it seriously.

Data Protection

All of the discussion above is quite apart from whether the email addresses should have been collected in the first place and then used for the purpose of sending emails. If in doubt, talk to your data protection manager.

Disk Space

I also have to put a short note in here about disk space. While most modern email systems will store a single copy of an email destined for multiple recipients on an email server, as soon as the email is copied off, forwarded or archived, a copy is made and the amount of space it takes up doubles. So, mass emails that have 1MB attachments can take up significant amounts of space if sent to a large number of people. And disk space is not free.

LSE resources

If you’re at the LSE and do want to send emails to large numbers of people, please see the LSE’s policy on internal email communications and the Conditions of Use for IT Facilities.