Why does my site run slowly when I send out newsletters?

Sites will run slowly if they suddenly encounter an amount of traffic that they aren't configured to handle. This is why distributed denial of service (DDoS) attacks, in which lots of traffic is pointed at a site, can be effective in temporarily bringing a site down.

Sometimes a site may slow down during a newsletter mail-out. This isn't because of loads of people instantly opening the emails and causing a traffic spike, but rather because of the email's content.

Email providers such as Gmail will scan links it finds in emails in order to protect the user from scams and malware. Instead of scanning the same link over-and-over again, Google will presumably create a database, so it knows which URLs have been marked safe and when.

This would mean that if you sent a newsletter out with 10 links in it to 1000 people, it would scan 10 links at most. Obviously, this would not slow a site down.

However, if you send emails via a marketing company who detect when links have been clicked, it is likely that links will go via a URL shortener owned by the marketing company. This is because to get tracking information, they need to send unique URLs to every user. This is why links in newsletters often have huge URLs with a lot of parameters (which arguably is bad for usability as it may look like a phishing attempt to a more cautious user).

Because of this, sending a newsletter with 10 links to 1000 people via tracking redirects would cause 10000 links to be scanned - you've just DDoSed yourself.

If this is a problem, the solutions are going to be:

• Stagger sending emails, if possible.
• Don't track email clicks, so that the links in your email are direct links to your site. UTM codes are usually enough to get you useful information.