Reduce the size of pictures and attachments

When you send a message that exceeds the message size limit for either your or the recipient's mail server, the message will be returned to you and not delivered. This is often called a "bounced" message.

Optimizing the size of pictures and attachments for e-mail helps to avoid exceeding the maximum message size limits associated with most e-mail accounts.

 Note    Messages increase in size while in transit through the Internet beyond the actual sum of the size of text, graphics, pictures, and attachments. Encoding of a message for transmission through the Internet leads to a size increase of approximately one-third. For example, if your Internet service provider (ISP) (ISP: A business that provides access to the Internet for such things as electronic mail, chat rooms, or use of the World Wide Web. Some ISPs are multinational, offering access in many locations, while others are limited to a specific region.) allows you to send messages up to 10 megabytes (MB) and you include a 9 MB attachment, you will probably exceed the maximum message size.

In addition to a per-message size limit, many e-mail accounts include a mailbox or account storage limit. Large attachments can not only fill a recipient's mailbox but increase your own Outlook data file size and mailbox. By default, a copy of each message that you send is saved to the Sent Items folder in Outlook.

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Reduce the size of picture attachments

There are two ways to reduce the size of pictures that you attach to e-mail messages in Outlook 2010:

  • Reduce the picture dimensions    Digital cameras can create very large images far in excess of the dimensions that most computer monitors can display full screen. Compressing the image to a smaller width and height can greatly reduce the file size. This option is available for pictures that are attached, but not displayed within the message body.
  • Compress the picture resolution    By decreasing the dots per inch (DPI), file size is reduced, but the quality of the image is also impacted. Displaying images on a computer monitor requires a lower DPI than images that are printed. If the recipient doesn’t need higher quality resolutions, use a lower setting. This option is available for pictures that appear within the message body.

In all cases, the original picture file saved on your computer hard disk or memory device is not modified. Only the copy of the picture being sent is reduced in size.

Picture files attached within Outlook

When you add attachments in Outlook, you can reduce picture attachments on a per-message basis. When you choose to resize large images, any attached image is reduced to a maximum resolution of 1024x768 pixels

 Note    If you embed the picture in the message body — the picture appears in the message — by using the Picture command in the Illustrations group, the image attachment resize feature is not available.

  1. Create a new e-mail message in Outlook.
  2. On the Insert tab, in the Include group, click Attach File.

 Tip    You can also drag and drop a picture from Windows Explorer. The picture file will be attached to the e-mail message.

  1. In the message window, click the File tab.
  2. Under Image Attachments, click Resize large images when I send this message.

Picture attachment resize options in the Backstage view

  1. Click the Message tab to return to your message.
  2. When you are finished composing your e-mail message, click Send.

Picture files sent from Windows Explorer with the Send To feature

When you use Windows Explorer to select picture files and then then create an e-mail message, you have multiple resize choices.

  1. Open Windows Explorer by clicking Start, and then double-clicking Computer.

 Note    Double-click My Computer in Windows XP.

Keyboard shortcut    To open Windows Explorer, press Windows logo key+E.

  1. Navigate to the folder that contains the pictures you want to send.
  2. Select a picture. To select multiple files, press and hold CTRL as you click each file.
  3. Right-click a selected file, point to Send To, and then click Mail Recipient.

In Windows 7, the Attach Files dialog box appears. In Windows Vista and Windows XP, a similar dialog box appears.

  1. In the Picture size list, click the image size that you want.

Resize picture attachment options

An estimate of the new file size appears.

A new Outlook message window appears with the attached picture.

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Reduce picture file sizes by reducing the resolution quality of picture attachments

 Note    This option is available only for pictures that appear in the body of a message.

When you do not need every single pixel (pixel: A single unit of measurement that your computer's display hardware uses to paint images on your screen. These units, which often appear as tiny dots, compose the pictures displayed by your screen.) in an image to get an acceptable version of it for your target destination, you can reduce or change the resolution. Reducing or changing the resolution can be effective with images that you have scaled to be smaller, because their dots per inch (dpi) actually increase in that case. Changing the resolution can affect image quality.

  1. Click the picture or pictures that you want to change the resolution (resolution: The fineness of detail in an image or text produced by a monitor or printer.) for.
  2. Under Picture Tools, on the Format tab, in the Adjust group, click Compress Pictures.

Adjust group on the ribbon

If you do not see the Picture Tools and Format tabs, make sure that you selected a picture. You may have to double-click the picture to select it and open the Format tab.

  1. To change the resolution for the selected pictures only and not all of the pictures in the document, select the Apply only to this picture check box.
  2. Under Target output, click the resolution that you want.

 Important    Compressing a picture to reduce the size of the file changes the amount of detail retained in the source picture. This means that after compression, the picture can look different than before it was compressed. Because of this, you should compress the picture before applying an artistic effect.

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Reduce the size of file attachments

The amount of reduction possible depends on the type of file format and content. For example, a Notepad .txt file will compress considerably. A Microsoft Word 2010 document in the .docx file format is already compressed; further compression will have little impact on the file size.

 Note    For more information specific to reducing picture files, see the section Reduce the size of picture attachments..

  1. Open Windows Explorer by clicking Start, and then double-clicking Computer.

 Note    Double-click My Computer in Windows XP.

Keyboard shortcut    To open Windows Explorer, press Windows logo key+E.

  1. Navigate to the folder that contains the file you want to send.
  2. Select a file. To select multiple files, press and hold CTRL as you click each file.
  3. Right-click the selection, point to Send To, and then click Compressed (zipped) Folder.
  4. Select the newly created compressed file.

The file name will match the original file's name but will have a different icon. If you have configured Windows to display file extensions, the file name will end with an extension of .zip.

  1. Point to Send To, and then click Mail Recipient.

A new Outlook message window appears.

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Best practices for size management when sending pictures and attachments

The following is a list of best practices to use when sending pictures and attachments:

  • Post or publish large attachments     If you're sending attachments or pictures to someone within your organization, use a file share on your computer or a shared network resource. You can include a link to that location in your e-mail message. Or, if your organization uses Windows SharePoint Services 3.0, post the attachments in a document workspace or in a SharePoint library and point users there. Either way, everyone uses only one copy of the files.
  • Limit your attachments to under 5 megabytes (MB)     This is a general guideline; for slower, dial-up connections you should use a much smaller size, such as 250 kilobytes (KB). If you must send larger attachments, verify the maximum size of the message that you can send. Your mail server administrator or ISP can tell you this. Likewise, ask the recipient what their maximum limit is. Finally, consider the recipient's Internet connection speed. Downloading a large attachment on a dial-up Internet connection can take a long time.
  • Send multiple attachments by using several e-mail messages     Multiple smaller messages have a higher likelihood of being delivered versus one large message. This technique might help you avoid per-message limits, but the recipient's mailbox limit can still be exceeded. Any messages received after a person's mailbox has reached its storage limit are typically rejected.
  • Use compressed graphic file formats     There are far too many graphic file formats to list here, but of the most commonly used, the best picture file formats for e-mail are .jpg, .png, and .gif. The largest graphics file formats are those that are not saved in a compressed file format, such as .tif and .bmp (the default file format of Windows Paint).
  • Use smaller original files     The size of a photo taken by a digital camera is typically large, even when saved in a compressed file format such as .jpg. It's not uncommon for a single picture to be several megabytes. Remember that the size of the e-mail message will increase by approximately one-third while in transit on the Internet. Use a lower resolution setting on your camera when taking a digital photo. Use compressed file formats such as .jpg. In a graphics program, crop photographs to the essential content.
  • Use a file compression utility     In addition to third-party utilities, Windows includes a file compress utility that uses the compressed .zip file format. Many attachment file formats can be reduced with the use of a compression utility. The amount of reduction will be minimal with some file formats that are already saved in a compressed format. For example, a Notepad .txt text file will reduce dramatically, while a .jpg image will not. The .jpg file format is already a compressed file format. You can find more information about using file compression in Windows Help.
  • Review your Sent Items folder     By default, a copy of each message that you send is kept in the Sent Items folder. This increases the size of your Outlook Data File (.pst), which can, with certain accounts, count against your mailbox size limit because the sent items are saved on your mail server.

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Applies to:
Outlook 2010