Why are Microsoft and Google frequently blocked?

Spamhaus, SpamCop and similar real‑time blacklists (RBLs) block entire IP ranges when they see a high volume of spam originating from them. Because both providers offer free email accounts that anyone can create, spammers automate the registration process and then use those accounts to send large volumes of junk mail. This results in a significant proportion of their mail being flagged as abusive.

• Spam volume: Roughly 35 % of global spam is traced to Google‑hosted domains (gmail.com, etc.), and just over 40 % to Microsoft‑hosted domains (outlook.com, hotmail.com, etc.).
• Server turnover: At any moment, about one‑quarter of the mail servers belonging to these providers are listed on one or more blacklists, often on several simultaneously.
• Why they stay blocked: Until the providers can stop automated account creation and bot‑driven spam, the blacklists will continue to list large portions of their infrastructure. Blocking them is a trade‑off – it reduces spam dramatically, even though it occasionally blocks legitimate, but rarely important mail.

What this means for you

If you are sending email from a Microsoft or Google address (e.g., a corporate address on Outlook/Google Workspace), your messages may be rejected or delayed if the sending IP or domain appears on a blacklist. This is not a fault of the recipient; it is a defensive measure by the receiving server.

Practical steps to resolve delivery problems

Use a proper dedicated business email provider with a good reputation. In Email, reputation is everything and picking the correct provider will ensure trouble free delivery. 

When to seek further help

You cannot seek further help, both google and Microsoft have no way to seek such help and unless you're using their enterprise tiers, they simply don't care.