Send and download email attachments with Nylas

Short summary

Nylas Email API supports two attachment schemas: JSON (base64-encoded, capped at 3MB total request) and multipart/form (binary, up to 25MB). The post covers sending attachments, the base64 inflation gotcha that causes seemingly-small files to fail, inline image content IDs, and downloading attachments via CLI. Practical rules guide when to switch from JSON to multipart.

• •JSON method caps at 3MB total request including base64 inflation; multipart handles up to 25MB
• •Base64 encoding inflates file size by ~33%, so switch to multipart before 3MB raw file size
• •Inline images require content ID wiring to render in HTML body rather than as separate attachments

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