Hey Ashwin - common pattern with HubSpot Sequences through M365 when DKIM isn't enabled. Good news: it's fixable without touching the DNS records that affect inbound mail. Quick mental model that might help: SPF, DKIM, and DMARC are the three records receiving filters check on OUTBOUND email. They're separate from MX records, which control INBOUND. Adding or fixing SPF / DKIM / DMARC won't stop you receiving mail. The change that broke inbound previously was almost certainly MX-related, which is a different category of fix. Three things to do, in order: 1. Enable DKIM in M365 (Exchange admin center → mail flow → DKIM, enable for your domain). M365 will generate two CNAME records (selector1._domainkey and selector2._domainkey) you publish at your domain host. New records - they don't conflict with anything existing. 2. Audit your SPF: confirm both Microsoft AND HubSpot are included in your domain's SPF TXT record. If you've got a lot of includes already, watch the 10-lookup limit (SPF fails silently if you exceed it). 3. Publish a DMARC record at p=none with a reporting address. Lets you watch for 7-14 days who's actually authenticating and who isn't before you raise enforcement. The Outlook spam-block usually clears within a few days of auth being clean, because the receiving filters stop classifying you as an unauthenticated sender. The 5-bounce trigger is M365 being conservative when it can't verify you. Happy to run a quick public-data scan on your sending domain offline if useful - DM me and I'll send back a one-pager with the specific findings.
On the deliverability piece - tool choice barely moves it. Lemlist, Apollo, Outreach, Smartlead all sit on top of the same underlying email infrastructure. Placement is driven by authentication (SPF/DKIM/DMARC alignment), warmup discipline, list quality, and sender reputation. None of which a platform's UI fixes. Evaluate Lemlist on what it actually controls: sequencing logic, personalization depth, LinkedIn integration, reporting, and how it handles inbox rotation under the hood. If deliverability is the actual problem you're solving, switching platforms won't get you there.
