Outlook emails not deliverable to yahoo and aol

Just to reiterate for you and all the people coming here, thinking Microsoft can fix this for you, they cannot. If you are using your own domain (aka: custom domain) for email hosted in M365, you need to work with your IT or your domain host, or do your own research to confirm that the necessary DNS records.

I find SPF records are the easiest to create and manage. You can look up your SPF record by doing a google search for "spf lookup". I most often use the checker from MX Toolbox. If you are using M365, your SPF should look something like this -

v=spf1 include:spf.protection.outlook.com ~all

At the bottom of the lookup, it will tell you "Reported by", this will tell you who is hosting your DNS, that is where the SPF record gets created / modified. You log in or reach out to that DNS hosting company, and create or edit the TXT DNS record for SPF there. Setting up DKIM and DMARC gets a little more complicated, and are not necessary if you have a valid SPF record, and turn off the SPF record for the "OnMicrosoft.com" domain which I outlined in my post on page 2 of this thread.

FOR ANYONE continuing to post to this thread looking for a solution, they only way the community can offer insight into your specific problem will be for you to post your domain name, then we can lookup the details and try to offer additional guidance.

It is a custom domain, but I'm not sure I'm comfortable saying my domain name (I'm sure I'm being paranoid). I will say that it is hosted by Microsoft365 and the domain was purchased through a 3rd party vendor (Nelnet, if it matters).

Perhaps you can answer this one question, do you use a custom domain name, for example: mycoolcompany.com

If that is correct, would you mind telling us the domain name? Do not post your entire email address. At the very least, we can tell you who is responsible for fixing the problem (your IT, Microsoft, AOL or Yahoo/Gmail).

I'm hoping you're wrong, because none of those acronyms you just posted mean anything to me. I'm an office administrator in a very small business, not an IT person.

You have a choice, wait forever or take action. If you use custom domain, they can't help you to fix the problem. You may be missing some or all necessary DNS records (SPF, DMARC, DKIM). You must fix that yourself. If you use outlook.com or hotmail.com domain, there is nothing you can do to fix it.