Spam Filtering Uses Many Signals
Receiving providers do not rely on one rule. They evaluate authentication, sending reputation, message content, user complaints, engagement, and technical behavior.
Authentication Matters
SPF, DKIM, and DMARC help prove that a message is authorized. Missing or broken authentication can reduce trust.
New Domains Have Little Reputation
A new domain or mail server may need time to build a positive sending history. Sudden large campaigns from a new identity can look suspicious.
Recipient Quality Matters
Sending to old, purchased, or invalid lists increases bounces and complaints. Use confirmed recipients and remove addresses that repeatedly fail.
Content Can Trigger Filters
Excessive capitalization, misleading subject lines, image-only messages, suspicious links, and poor HTML can hurt placement. Clear business language usually performs better.
Shared Reputation Can Affect Delivery
On shared mail systems, providers monitor overall behavior and take action against abusive users. Dedicated email services may offer more control for large-volume campaigns.
Ask Recipients To Add The Address
For expected business communication, asking customers to add the sender to their contacts can improve recognition.
Check More Than One Provider
A message may reach Gmail but not Outlook, or the reverse. Test several major providers and review bounce messages for specific clues.