Every email service provider treats hard bounces differently. In most cases, a hard bounce will never be valid ever again. In select cases, it may just mean that the address is currently unavailable but will be available at some point later.
Here’s a personal story about why it doesn’t make a lot of sense to bounce remove after the first attempt.
I purchased my personal domain name in 1998 and have used it for select personal email relationships ever since. I had a problem with my domain registrar a couple years ago that involved them accidentally expiring my domain without notifying me. It then took weeks to get it fixed. In the meantime, all personal email to me hard bounced. Some of my most important contacts reached out to me through other channels, a few even sending snail mail informing me of the bounced email.
While this situation is rare, it is just one of many reasons why emails hard bounce and yet will be valid once again in short order.
In the past, ISPs used to focus on hard bounces as a critical anti-spam metric. With today’s sophisticated filters focused primarily on complaints and other data, very few ISPs see a reasonable (<5%) hard bounce rate as an indicator of spam as long as the other performance metrics are also in line with legitimate email.
Some additional tips when considering bounce removal rules:
- Every ISP is different, therefore a liberal bounce rule at less sophisticated ISPs (like those without real-time complaint data) could result in deliverability problems.
- Re-mailing bounces again is not the same as ‘re-trying’ a message. If the address is invalid now, it likely won’t be valid again the same day or even a few days from now. Wait a week or more before re-mailing that user.
- Never re-mail bounces more than a few months old. Some ISPs turn bad data into spamtraps, which are used as an anti-spam filter. In some cases, ISPs will share defunct addresses with 3rd party blocklists like Spamhaus. In other cases, an ISP may recycle that address to another user.
- If the relationship is really important (or if you have the resources), consider a personalized snail mail effort following a bounce. I was pleasantly surprised about the letters from my commercial relationships and valued those relationships even more as a result.