We've been using Zoho Campaigns for the last year or so. Since the turn of the year, we've experienced a significant drop in our open rate (2-3%) without any real explanation. Our content is very much the same, and we felt our subject titles were not much different and  so I don't understand exactly why our open rate is so much lower. 

We did some tests at our end, running the same campaign on ZOHO campaigns and on Mailchimp - and found that on Mailchimp, we had an open rate of 13.7% - meanwhile on ZOHO campaigns, it was 8.7% which is quite a big difference!

And so I wonder if you can offer any personalised  insight or advice on how we can improve our open rates?

Thanks in advance!