Why Maximum Email Attachment Size is 50MB
This article explains why iCoreHosting enforces a maximum attachment size of 50MB for outgoing and incoming emails, including technical limitations, global email standard practices, and how different providers (Gmail, Outlook, Yahoo, Zoho) handle large attachments.
Table of Contents
- Service Direction / Introduction / Scope
- Service Transparency
- Definitions
- Why Email Attachment Limit is 50MB
- Common Mistakes
- Limitations (Gmail, Yahoo, Outlook, Zoho and Others)
- FAQ
- Use Case
- Summary
Service Direction / Introduction / Scope
iCoreHosting sets a standard maximum email attachment size of 50MB across all Business Email Hosting and Web Hosting plans. This policy follows global email delivery standards to maintain optimal server performance, ensure high deliverability, and avoid rejection by external email providers.
Service Transparency
Email is not designed for transferring very large files. When attachments become too large, emails are rejected by external providers, cause server congestion, or increase the risk of delays and failures. The 50MB limit ensures stable performance for all users.
Definitions
Attachment Size: The file size before encoding.
MIME Encoding: Email servers convert attachments using Base64 encoding, increasing the size by approximately 30 to 40 percent.
SMTP Limit: The maximum email message size allowed by a mail server.
Why Email Attachment Limit is 50MB
Although the user uploads a 50MB file, email servers must encode the file into Base64. This process increases the final email size to approximately 65MB – 70MB.
Many receiving mail providers such as Gmail, Yahoo, Microsoft Outlook, and Zoho enforce strict message size limits. If the final encoded size exceeds their limits, the email will be rejected before delivery.
Therefore, iCoreHosting’s 50MB limit ensures maximum compatibility and the highest delivery success rate.
Common Mistakes
• Uploading a 50MB file and assuming the final email is still 50MB.
• Sending multiple attachments that exceed the combined message limit.
• Trying to send oversized files to external providers that enforce lower limits.
• Confusing mailbox space (storage) with attachment size (SMTP limit).
Limitations (Gmail, Yahoo, Outlook, Zoho and Others)
Different email providers enforce their own maximum message size limits:
- Gmail: Max 25MB per email (encoded). Files above this auto-upload to Google Drive.
- Outlook / Hotmail: Max 20–25MB depending on region.
- Yahoo Mail: Max 25MB.
- Zoho Mail: Max 30MB.
- Corporate servers: Many impose 10MB or 20MB limits as default for security and performance.
This means even if iCoreHosting allows 50MB, the recipient may reject anything above 20–25MB.
FAQ
Q: Why cannot iCoreHosting increase to 100MB?
A: Most major email providers will reject emails larger than 25–30MB. Increasing the limit only increases failed deliveries.
Q: Can I send 50MB to internal staff?
A: Yes, internal emails within the same server may succeed, but external delivery is not guaranteed.
Q: What is the best way to send large files?
A: Use iCoreHosting File Sharing, Google Drive, Dropbox, WeTransfer, or send as a download link.
Q: Why does my 40MB file become 55MB?
A: Base64 encoding adds 30–40 percent extra size. This is normal email behaviour.
Use Case
A user sends a 40MB PDF to a client using Gmail. After encoding, the message becomes around 52MB. Gmail rejects it due to exceeding its 25MB receiving limit. The user switches to a download-link method (Google Drive / iCoreHosting File Sharing) and the file is delivered successfully.
Summary
The 50MB attachment limit is set to ensure maximum email deliverability across all global providers. Due to Base64 encoding, a 50MB file becomes around 65–70MB, which often exceeds the limits of Gmail, Yahoo, Outlook, and other platforms. For large file sharing, users should always use cloud storage links or file-sharing services.
