Does anyone else have constant problems with emails being undeliverable? One month all my voices are sent out just fine, the next month half of them are undeliverable

Yes — you're definitely not alone. Many users of QuickBooks Online (QBO) have reported intermittent issues with invoice emails being marked as undeliverable or not reaching clients, and this seems to be a recurring issue, especially around:

• Changes in QuickBooks' email server IPs

• Tightened spam filter rules by recipient mail servers (like Gmail, Outlook)

• Missing or misconfigured sender domain settings (SPF, DKIM, DMARC)

• Clients accidentally marking previous emails as spam