You might see a new error message in an email invitation or email trigger message like "All external links in the Body must be https:// and not http://". This change was made in October 2024 and is part of a larger piece of work in improving the deliverability of email messages.
This will affect any modifications to existing messages but not (currently) any messages that are already saved in the system.
Why? Email Providers are expanding their set of tools and rules for deciding whether to trust incoming email. Although there is nothing inherently wrong with a small message, an urgent call-to-action or http links, these are reasonably good indicators of poor email quality and are likely the sorts of things that SPAM or Phishing emails will do.
In line with the recommendations of the Certified Senders Alliance, we have taken the decision to now require all external links to be https, which should not be an issue and will be easy to check and/or setup if necessary at your end. Public links are usually https anyway so it hopefully won't be too much inconvenience for you.