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.