Handling attachments
On this page you will find information on how to handle attachments in general, blocked attachments, and alternatives for sending emails with large attachments or large amounts of data.
Handling attachments
Email attachments can contain potentially dangerous files (e.g., malware). Especially in the case of emails that seem suspicious or unusual, check whether it is a legitimate email and the correct attachment.
In an emergency, check with the sender of the email. You can read about how to recognize suspicious attachments and emails and how to deal with them in the article Suspicious Emails.
Attached files with the extensions .exe, .msi, .bat, .zip, or .rar can be particularly dangerous. However, other file types containing macros, such as .doc, .docx, and .pdf, can also be used.
To minimize the potential danger of attachments, RWTH filters files that are recognized as dangerous or contain potentially dangerous macros in advance. You can find more information on this in the article Email macro filter.
Even with filtering, not all suspicious files can be found. Before you save/download or open attachments, you can also check them using antivirus software or sites such as Virustotal.
Blocked attachments in Outlook
Outlook already blocks access to selected email attachments for security reasons. Other email clients have similar rules. We would ask you to check whether this applies to the email client you use.
The settings can be adjusted independently, with three options available:
- The attachment is completely blocked: The recipient is only shown that an attachment is present, but the user cannot access it.
- The attachment must be downloaded and saved before it can be executed and opened.
- The attachment can be opened directly by double-clicking on it.
You can remove certain attachment types or files with specific file extensions from this filter if legitimate attachments with these file extensions are blocked. However, this also increases the risk.
To change the settings, follow these steps:
Step 1
Close all active Outlook instances.
Step 2
Search for regedit (alternatively Registry Editor) using Windows Search or Windows Run and start the application.
Step 3
This will open the Registry Editor.
Now navigate to the following path:
HKEY_CURRENT_USER\Software\Microsoft\Office\Version Number\Outlook\Security
The version number may vary depending on your version of Microsoft Office or Outlook. Then select Outlook\Security. For example:
- Outlook 2000:
[HKEY_CURRENT_USER\Software\Microsoft\Office\9.0\Outlook\Security] - Outlook 2002:
[HKEY_CURRENT_USER\Software\Microsoft\Office\10.0\Outlook\Security] - Outlook 2003:
[HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Outlook\Security] - Outlook 2007:
[HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Outlook\Security] - Outlook 2010:
[HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Security] - Outlook 2013:
[HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Security]
Step 4
Now click Edit -> New -> String Value and enter Level1Remove.
This will create a folder named Level1Remove.
Step 5
Now double-click to open the Level1Remove folder and enter the file extensions you would like to keep. These will then be removed from Outlook's internal filter and accepted.
Please remember to separate multiple file extensions with a “;” when activating them.
Confirm your entry by clicking OK.
Step 6
Then close the Registry Editor to save the changes.
You can now reopen Outlook and the previously blocked file types will now be enabled and can be opened.
Sending large amounts of data
If you want to send large amounts of data with file attachments by email to multiple addresses or distribution lists, this can quickly lead to problems:
- Depending on the number of addressees (distribution lists typically contain thousands of e-mail recipients), the data traffic is very high.
- Well-known email providers usually allow a total email size of 20MB to 40MB to keep the load correspondingly low. This applies to sending and receiving e-mails.
- At RWTH Aachen University the maximum mail size is 25MB (mail text + attachment). This is to ensure that e-mails can be delivered inside and outside RWTH Aachen University.
- Mailboxes usually offer limited storage space. They are therefore considered unsuitable for storing files.
It is therefore a good idea to make files available in alternative ways. For example: you can make files available via a download link to a data storage device. In addition to the above-mentioned hints, this can also lead to more security in communication.
If, for example, you already use data storage services when working on collaborative projects, these often offer integrated solutions for sharing data.
The use of such a service is particularly recommended when dealing with documents, as it ensures that all recipients always have access to the latest version of a document and that there are not several versions in circulation, e.g., as email attachments.
As alternatives, you can use the following methods at RWTH:
