Email deliverability is a poorly understood subject. It is easy to get distracted or confused by the mass of articles on the web about email marketing and deliverability. However, most email marketing experts consider following “best practices” to be your best bet.
About 40% of legitimate commercial and financial emails never reach the inbox, and email filtering is a constantly changing battleground for most financial institutions. Some banks decide to send email into a “black hole”. Essentially, this makes it look like your email was accepted and delivered to the end-user recipient, while the email never makes it to its destination. The bank’s mail system just accepts the email and dumps it. The problem is, you think your email was delivered when, actually, it wasn’t. So you have no reason to believe there is a problem with the email, because no bounce codes were returned.
This is one of those impossible problems to deal with when it comes to email delivery: how can you remove a hard bounce if you don’t know that it was a hard bounce, invalid and undeliverable, and the ISP doesn’t tell you?