A recent email of ours had a higher undeliverability rate than usual. With everything else being the same, this could only be because of the content. While we can have a guess at what triggered recipients’ spam filters, there was nothing obvious, so the lesson from the story is that it’s easy to accidentally include a term in an email which could hurt its deliverability.
From a sender’s point of view, there’s not much we can do except avoid terms that might be shared with spam or other less savoury emails. However, from a recipient’s point of view, it’s always a good idea to ensure our email ‘whitelists’ are kept up to date. Whenever I get an important email, I always add the sender’s address to a filter ensuring their emails never get sent to the spam folder in future, whatever their content. Some email clients (such as GMail) let you add entire domains to the ‘never send these to spam’ filter. I’d certainly include as many customers as possible on this list.
Most email clients have decent instructions online explaining how to set up and maintain a ‘whitelist’ or ‘never send these to spam’ filter. If you’re at a larger company where someone else is responsible for IT services, you should check with them on how suspected spam is handled. In some systems, it can be deleted before reaching your spam folder.