Do attachments affect deliverability?

Attachments can negatively impact deliverability, especially for marketing and bulk email. They trigger additional scrutiny from spam filters and security systems.

Deliverability concerns:

Spam score impact: Attachments add points to spam scores. Unsolicited email with attachments is a common spam pattern.

Malware scanning: Security systems scan attachments for viruses and malware, adding processing time. Some systems quarantine or reject emails with certain attachment types.

File type restrictions: Many providers block executable files (.exe, .bat, .js) entirely. Even zip files face extra scrutiny.

Size limits: Large attachments may cause rejection or delays.

Content filtering: Password-protected archives often get blocked because scanners can't inspect them.

Best practices for marketing email:

Avoid attachments in bulk email entirely

Link to files hosted on your website or cloud storage instead

If attachments are necessary, use common, safe types (PDF, images)

Keep sizes small

Never send executables or archives containing executables

Transactional emails (invoices, receipts) may need attachments; they typically have better treatment due to expected nature.

Cargo inspection is stricter for unknown vessels carrying sealed crates. Open, linkable cargo passes through faster.