I currently offer email subscriptions on my blog, something I coded myself in PHP.
People sign up on the blog using their email address. I send them an email with a link to verify their email address and once verified, they get an email whenever a new post is published. I only publish about 4 or 5 posts in a month and every email sent has an unsubscribe link which unsubscribes them right away if they wish. I hate spam so I definitely don't want to send anyone email that they don't want. I'm constantly checking to see if any of the emails bounce (nothing does) and would remove them from the list right away if there was ever a problem. I'm presently not having any problem with the emails being delivered and as far as I know, they're not ending up in people's spam/junk folders. I've set up my VPS box with SPF and DKIM, SSL only, etc… I currently have just under 200 email subscribers.
I'm wondering, is there any reason not to sign these subscription emails with an s/mime certificate? Would it improve deliverability? Or just give people the peace of mind of knowing that the email did in fact come from me?
Also, what about for email receipts? I'm presently working on updating another site, which will have an e-commerce component to it (via Stripe), so I'll be sending a lot of email receipts (I hope!), and also an email newsletter through that site also.
I know that s/mime is not that popular/wide-spread, so would sending these emails signed be a bad idea? (Not encrypted, just signed.) I don't see anyone else doing this, so I'm wondering if it's a bad idea? (Or why isn't anyone else doing it?)