Welcome to Sunday Funday: AI vs AI — a new weekly experiment on the Engagor blog.
Here's the concept: every Sunday, we take two AI agents — one playing a junior deliverability expert, the other a seasoned senior — and give them an email deliverability topic. No script. No human editing the conversation. We just hit "go" and see what happens.
Think of it like a sparring match between two email nerds. Except they never get tired, never lose patience, and occasionally call in a veteran colleague for backup.
This is Episode 1. We're starting with a classic: a sudden Gmail deliverability drop. Let's see how the AIs diagnose it.
Got a topic you want our AI agents to tackle next week? Drop it in the comments or DM us on LinkedIn.
This Week's Topic
"Why did my Gmail deliverability suddenly drop?"
The Conversation
Hey Hassan! So your Gmail deliverability tanked recently—did anything change on your end, like the volume of emails you're sending or maybe your sender domain setup?
Hey Nina! Yeah, it's been frustrating—deliverability dropped like 20% last week. Honestly, I'm not sure what triggered it since we haven't made any major changes to our sending volume or domain config that I'm aware of... could it be something like authentication issues creeping in, or maybe Gmail's algorithms got stricter?
Good questions—let's dig in. First, quick check: are you monitoring your SPF, DKIM, and DMARC records? Sometimes those silently break when DNS gets updated. Also, what does your bounce rate look like right now versus last week—hard bounces, soft bounces, or spam complaints spiking?
Good point—I actually checked our DNS records yesterday and everything looked fine, SPF and DKIM both passing. But honestly, I'm not 100% confident I'd catch a subtle DNS issue... should I be running a more detailed authentication audit?
As for bounces, let me peek at our dashboard real quick—looks like our hard bounces stayed pretty flat (~2%), but soft bounces jumped from like 3% to 8%, and spam complaints went up slightly too (0.08% to 0.15%). Does that pattern tell you anything?
Ah, now we're getting somewhere—that soft bounce spike is the real clue here. Hard bounces staying flat means your list quality didn't suddenly tank, but soft bounces jumping to 8% usually means Gmail's rate-limiting you or flagging your IP as suspicious. Did you check your sender reputation on tools like Google Postmaster Tools or Barracuda yet? That'll show you exactly what Gmail thinks of your IP.
Ohhh yeah, that makes sense—rate-limiting would explain the soft bounces! I haven't checked Postmaster Tools yet, let me look... okay, so I'm pulling it up now and it shows my authentication is passing, but my domain reputation is sitting at "Low" and there's a warning about "Suspicious sending patterns" flagged in the last 7 days.
That's weird though—we didn't intentionally change our sending patterns... could this be a compromise, or is it more likely just Gmail being overly cautious about something we did?
Hold up—"suspicious sending patterns" without you changing anything is a red flag. Quick questions: Did you send to any new recipient lists, maybe bought a list or added a segment you hadn't mailed before? Also, check your bounce management—are you still mailing to addresses that keep soft-bouncing, or did something go wrong with your suppression list?
Good catch—we did onboard a new partner list like 10 days ago, maybe 50k addresses? But we ran it through validation first, so I didn't think it'd be an issue... though now I'm wondering if the validation tool was actually thorough enough, or if we just got unlucky with the quality.
And wait, for the bounce management—let me check our suppression settings real quick... oh interesting, it looks like our soft bounce retry logic might've gotten reset somehow? We're retrying soft bounces up to 7 times over 2 weeks instead of our usual 3 attempts. Could mailing to the same soft-bouncing addresses repeatedly be what's triggering Gmail's "suspicious" flag?
Bingo—that's likely your culprit right there. Hammering soft-bouncing addresses 7 times looks like spam behavior to Gmail's filters, even if you're being "legitimate." Roll that back to 3 retries immediately, and also audit that new partner list—even validated lists can have stale or risky addresses. What's your typical complaint rate on that 50k batch compared to your house list?
Oh man, that makes total sense—I feel dumb for not catching that! Let me pull the complaint rate on that partner list real quick... okay, so the partner batch is sitting at 0.3% complaints versus our house list at like 0.08%. That's way higher, yeah?
Should I just pause sending to that partner list entirely while we clean it up, or would it be safer to slow down the send volume first and see if the reputation recovers?
Nina and Hassan, here's what you need to do immediately:
First: Roll back that soft-bounce retry logic from 7 to 3 attempts right now—that's almost certainly what triggered Gmail's spam filters, since repeatedly hitting the same bouncing addresses mimics abusive sending patterns.
Second: Pause the 50k partner list entirely (0.3% complaint rate is 3-4x higher than acceptable and indicates poor list quality), then run it through stricter validation or get a refund from your partner—don't just slow down sends, because you're still damaging your sender reputation with every message to that bad data.
Your house list reputation should recover within 3-5 days once you fix the retry logic and stop the partner batch.
Exactly—pause that partner list entirely, don't just slow down. A 0.3% complaint rate is poison for your domain rep, and Gmail won't forgive you gradually. Fix the retry logic first, cut the bad list, then monitor Postmaster Tools over the next few days—you should see reputation climb back within 3-5 days once those signals clear. Keep me posted on how it recovers!
Okay, got it—pulling the trigger on both of those right now. Pausing the partner list completely and rolling back the retry logic to 3 attempts. Thanks Nina, this was super helpful—I was totally overthinking it when it was just those two things compounding on each other!
I'll monitor Postmaster Tools daily and let you know when reputation starts bouncing back. Appreciate you walking me through the diagnosis!
Perfect—you've got this. Check Postmaster Tools in a couple days and let me know how it looks. Good troubleshooting!
Key Takeaways
What the AIs figured out:
- Soft bounce spike (3% to 8%) was the key diagnostic signal — hard bounces staying flat ruled out list quality decay, pointing instead to Gmail rate-limiting
- Aggressive retry logic (7 attempts instead of 3) looked like spam behavior — repeatedly hitting the same bouncing addresses mimics abusive sending patterns
- The new partner list had a 0.3% complaint rate — that's 3-4x higher than the house list and poison for domain reputation
- The fix was straightforward — roll back retry logic to 3 attempts, pause the toxic partner list entirely, and wait 3-5 days for reputation recovery
- Google Postmaster Tools was the diagnostic tool that confirmed the problem — domain reputation at "Low" with "Suspicious sending patterns" flagged
That's a wrap on Episode 1 of Sunday Funday: AI vs AI.
Same time next Sunday. Different topic. Same two AIs who definitely don't need coffee breaks.
Got a topic you want Hassan and Nina to tackle next? Drop it in the comments or DM us on LinkedIn. We're taking requests.
See you next Sunday.
