# Limitations ## Maximum Recipients Each email can have a maximum of **50 recipients** combined across the `to`, `cc`, and `bcc` fields. This limit applies to both the REST API and SMTP relay. | Field | Description | |-----------|------------------------------| | `to` | Primary recipients | | `cc` | Carbon copy recipients | | `bcc` | Blind carbon copy recipients | | **Total** | Maximum 50 combined | :::warning Emails exceeding 50 recipients (combined) will be rejected. For larger recipient lists, use the [batch sending endpoint](/docs/api-reference/sending/send#send-multiple-emails-in-a-batch) which supports up to 500 recipients per request. ::: This limit aligns with transactional email best practices. Transactional emails (receipts, notifications, password resets) are typically sent to a small number of recipients. If you need to send to larger lists, consider: - Using the **batch API** for sending the same email to multiple recipients - Splitting large recipient lists into multiple API calls - Using broadcast routes for marketing or newsletter-style emails ## Email Size Limit The maximum size for an email message (including all attachments) is **25MB**. This limit includes: - The email body (HTML and plain text) - All attachments (base64 encoded) - Headers and metadata :::warning Emails exceeding 25MB will be rejected with an error. Consider using external file hosting services for large files and including download links in your email instead. ::: ## Blocked Attachments For security reasons, certain file types are blocked from being sent as attachments. These restrictions help protect recipients from potentially malicious files. ### Blocked File Types The following table lists all blocked file extensions and their associated MIME types, organized by category: #### Executable Files & Applications | Extension | MIME Type(s) | Description | |-----------|----------------------------------------------------------------------------------------|-----------------------------| | `.exe` | `application/x-msdownload`, `application/x-executable`, `application/octet-stream-exe` | Windows executable | | `.com` | `application/x-msdownload`, `application/x-msdos-program` | DOS command file | | `.app` | `application/x-ms-application` | Application file | | `.msi` | `application/x-msi`, `application/x-ms-installer` | Windows installer package | | `.msp` | `application/x-msi` | Windows installer patch | | `.mst` | `application/x-msi` | Windows installer transform | | `.gadget` | `application/gadget`, `application/x-gadget` | Windows gadget | | `.dll` | `application/x-msdownload` | Dynamic link library | | `.jar` | `application/java-archive` | Java archive | #### Script Files | Extension | MIME Type(s) | Description | |-----------|------------------------------------------------------------------------------------------|----------------------------| | `.bat` | `application/x-bat`, `application/x-cmd` | Batch file | | `.cmd` | `application/x-cmd`, `application/x-bat` | Command script | | `.ps1` | `application/x-powershell`, `text/x-powershell` | PowerShell script | | `.ps1xml` | `application/x-powershell` | PowerShell XML | | `.ps2` | `application/x-powershell`, `text/x-powershell` | PowerShell v2 script | | `.ps2xml` | `application/x-powershell` | PowerShell v2 XML | | `.psc1` | `application/x-powershell` | PowerShell console file | | `.psc2` | `application/x-powershell` | PowerShell v2 console file | | `.vb` | `application/x-vb`, `text/vbscript` | Visual Basic file | | `.vbs` | `application/x-vbs`, `text/vbscript` | VBScript file | | `.vbe` | `application/x-vbe`, `text/vbscript` | Encoded VBScript | | `.js` | `application/javascript`, `application/x-javascript`, `text/javascript`, `text/x-script` | JavaScript file | | `.jse` | `application/x-javascript`, `text/jscript` | Encoded JavaScript | | `.ws` | `text/x-script` | Windows script | | `.wsf` | `text/x-script` | Windows script file | | `.wsc` | `text/x-script` | Windows script component | | `.wsh` | `text/x-script` | Windows script host | | `.sh` | `application/x-shellscript`, `application/x-sh` | Shell script | | `.csh` | `application/x-csh` | C shell script | | `.ksh` | `application/x-shellscript` | Korn shell script | | `.asp` | `application/x-asp`, `application/asp`, `text/asp`, `text/x-asp` | Active Server Page | #### System & Configuration Files | Extension | MIME Type(s) | Description | |-----------|-----------------------------------------------------|------------------------| | `.sys` | `application/x-sys`, `application/octet-stream-sys` | System file | | `.cpl` | `application/x-msdownload` | Control panel item | | `.scr` | `application/x-msdownload` | Screen saver | | `.reg` | `application/x-reg` | Registry file | | `.inf` | `text/plain` | Setup information file | | `.crt` | `application/x-crt` | Certificate file | | `.cer` | `application/x-crt` | Security certificate | | `.der` | `application/x-crt` | DER certificate | #### Microsoft Office & Access | Extension | MIME Type(s) | Description | |-------------|-------------------------------------------------------|--------------------------| | `.mdb` | `application/x-msaccess`, `application/vnd.ms-access` | Access database | | `.mde` | `application/x-msaccess` | Access compiled database | | `.mda` | `application/x-msaccess` | Access add-in | | `.mdt` | `application/x-msaccess` | Access data file | | `.mdw` | `application/x-msaccess` | Access workgroup | | `.mdz` | `application/x-msaccess` | Access wizard | | `.accdb` | `application/x-msaccess` | Access 2007+ database | | `.ade` | `application/x-msaccess` | Access project extension | | `.adp` | `application/x-msaccess` | Access project | | `.mad` | `application/x-msaccess` | Access module | | `.maf` | `application/x-msaccess` | Access file | | `.mag` | `application/x-msaccess` | Access diagram | | `.mam` | `application/x-msaccess` | Access macro | | `.maq` | `application/x-msaccess` | Access query | | `.mar` | `application/x-msaccess` | Access report | | `.mas` | `application/x-msaccess` | Access stored procedure | | `.mat` | `application/x-msaccess` | Access table | | `.mau` | `application/x-msaccess` | Access user | | `.mav` | `application/x-msaccess` | Access view | | `.maw` | `application/x-msaccess` | Access web | | `.pub` | `application/x-mspublisher` | Publisher document | | `.vsmacros` | `application/vnd.ms-vsmacros` | Visual Studio macros | #### Web & Browser Files | Extension | MIME Type(s) | Description | |-----------|---------------------------|-------------------| | `.hta` | `application/hta` | HTML application | | `.htm` | (when containing scripts) | HTML file | | `.html` | (when containing scripts) | HTML file | | `.url` | `text/x-url` | Internet shortcut | | `.mhtml` | Various | Web archive | #### Help & Documentation | Extension | MIME Type(s) | Description | |-----------|----------------------------------------------------|-----------------------| | `.chm` | `application/vnd.ms-htmlhelp`, `application/x-chm` | Compiled HTML help | | `.hlp` | `application/winhlp` | Windows help file | | `.its` | Related to help files | Internet document set | #### Shell & Shortcuts | Extension | MIME Type(s) | Description | |-----------|----------------------------------|--------------------------| | `.lnk` | `application/x-ms-shortcut` | Windows shortcut | | `.pif` | `application/x-pif` | Program information file | | `.shb` | Shell file | Shell scrap object | | `.shs` | Shell file | Shell scrap object | | `.scf` | `application/x-explorer-command` | Windows Explorer command | | `.sct` | `text/scriptlet` | Windows script component | | `.xnk` | Exchange shortcut | Exchange shortcut | #### Installer & Package Files | Extension | MIME Type(s) | Description | |-----------|---------------------------------|---------------------------| | `.ins` | `application/x-internet-signup` | Internet settings | | `.isp` | `application/x-internet-signup` | Internet service provider | | `.lib` | `application/x-archive` | Library file | | `.msc` | `application/x-msc` | Management console | | `.ops` | Office profile | Office profile settings | | `.pcd` | Photo CD | Photo CD image | | `.prg` | Program file | Program file | | `.fxp` | FoxPro | FoxPro compiled | #### Visual Studio & Development | Extension | MIME Type(s) | Description | |-----------|-------------------------|-----------------------| | `.vss` | `application/vnd.visio` | Visio stencil | | `.vst` | `application/vnd.visio` | Visio template | | `.vsw` | `application/vnd.visio` | Visio workspace | | `.vxd` | Virtual device | Virtual device driver | #### Media Files | Extension | MIME Type(s) | Description | |-----------|----------------------------|--------------------| | `.wmz` | `application/x-ms-wmz` | Windows Media skin | | `.emf` | `application/x-msmetafile` | Enhanced metafile | #### FoxPro Files | Extension | MIME Type(s) | Description | |------------|---------------------|------------------------| | `.bas` | BASIC source | BASIC source code | | `.prf` | Settings file | Profile settings | | `.plg` | Plugin file | Plugin file | | `.msh` | Script shell | Microsoft Shell | | `.msh1` | Script shell | Microsoft Shell v1 | | `.msh2` | Script shell | Microsoft Shell v2 | | `.mshxml` | Script shell XML | Microsoft Shell XML | | `.msh1xml` | Script shell v1 XML | Microsoft Shell v1 XML | | `.msh2xml` | Script shell v2 XML | Microsoft Shell v2 XML | #### Temporary Files | Extension | MIME Type(s) | Description | |-----------|--------------|----------------| | `.tmp` | Various | Temporary file | #### Miscellaneous | Extension | MIME Type(s) | Description | |----------------|--------------------------------|------------------------| | `.application` | `application/x-ms-application` | ClickOnce deployment | | `.obd` | Office binder | Office binder document | | `.mvb` | Multimedia viewer | Multimedia viewer file | | `.vps` | Virtual private server | VPS file | ### Additional MIME Type Restrictions The following MIME types are also blocked: - `application/octet-stream` (for executable files) - `application/x-msdownload` - `application/x-ms-installer` - `application/x-msdos-program` - `application/x-msscript` - `application/x-ms-shortcut` - `application/x-ms-wmz` - `application/x-msmetafile` - `application/x-msbinder` - `application/x-msmediaview` - `text/scriptlet` ### Why These Restrictions? These file types are blocked because they can: - Execute code automatically when opened - Exploit vulnerabilities in email clients or operating systems - Bypass security measures through social engineering - Contain macros or scripts that could harm the recipient's system - Be used to spread malware or ransomware :::tip Most business documents (PDF, DOCX, XLSX), images (JPG, PNG, GIF), and common file formats are allowed. The restrictions focus on executable and script files that pose security risks. :::