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An email attachment is a file sent alongside an email message that recipients can download, view, or save. Attachments can include documents, images, videos, spreadsheets, PDFs, and other file types. They are encoded using MIME (Multipurpose Internet Mail Extensions) to ensure safe transmission across email systems.
Proper attachment handling is critical for email security and deliverability. Large or suspicious attachments can trigger spam filters, causing your emails to be blocked or sent to junk folders. Many email providers scan attachments for malware, and certain file types like executables (.exe) are blocked entirely. Understanding attachment limitations helps you communicate effectively while maintaining good sender reputation.
When you attach a file to an email, the email client converts the binary file data into a text format using Base64 encoding. This encoded data is then included in the email body with MIME headers that specify the file type, name, and encoding method. The receiving email client reads these headers, decodes the Base64 data, and reconstructs the original file for the recipient to download or view.
Most email providers limit attachments to 20-25MB. Gmail allows up to 25MB, while Outlook permits 20MB. For larger files, use cloud storage services like Google Drive, Dropbox, or OneDrive and share the link instead.
Attachments may be blocked due to file type restrictions (executables, scripts), size limits, or security scans detecting potential malware. Some corporate email systems also block specific file extensions. Try using a different format or sharing via cloud storage.
Yes, attachments can impact deliverability. Large attachments increase email size, which may trigger spam filters. Suspicious file types can cause emails to be quarantined. For marketing emails, consider using hosted images and links rather than direct attachments.
Standard email attachments are not encrypted by default and can be intercepted in transit. For sensitive files, use password-protected documents, encrypted email services, or secure file-sharing platforms with access controls.
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