I occasionally use an online CRM service called Relenta, it’s good but perhaps too much for my present basic needs. However it was thanks to their Email newsletter I’m now aware Yahoo and AOL have effectively ended the practice of businesses using Yahoo or AOL accounts with things like eVites and 3rd party services such as Relenta!
These “Domain-based Message Authentication, Reporting & Conformance” (DMARC) changes and related Sender Policy Framework (SPF) checks could be preventing your important marketing and service emails from being delivered!
Of course I would never recommend using a free web mail service for business use when domain based email can be set up for relatively little cost (from SMH Tech anyway). So if you use Yahoo or AOL, or others such as Gmail, Hotmail/Outlook.com et al, I recommend you check your mail is getting through and if your provider is making changes to its DMARC or SPF systems!