Bounced Emails with Error Message 550 5.7.1_ETR

Owned by McKenna Duffy (Deactivated), created
Aug 27, 2021
2 min read

Problem

If you attempt sending email to a seattleu.edu email address and receive a bounce message with the following error message:

This message was rejected because it contains an attachment that could be malicious. Visit the SU site to see blocked files.

This is an indication that the attachment you included in your message is not an allowed message attachment type.

As part of Seattle University's commitment to cyber security, we block certain file extensions that are sent through campus email. These file extensions are a potential security risk because they could spread viruses through personal and University computers.

Files may also be blocked if the systems detect an embedded program within a file, no matter the file’s extension.

Examples

  • An excel file might still have a macro inside of it even if the extension is not .xlm.

  • Someone removes the extension of an executable (exe) file before sending it as an attachment.

  • A zip file contains an executable (exe) file.

Additionally, Microsoft also blocks some of these file types and we cannot override Microsoft’s blocks as we use their systems. The types of files blocked by Microsoft are constantly growing as malicious actors adapt their attack techniques.

Alternatives

Here are some alternatives to sending the files via email.

Blocked File Extensions in Office 365

Below is the list of identified file types that are blocked as part of this security measure. This is not a comprehensive list, as stated above, Microsoft also adds other file types to their own blocks regularly as a part of routine cyber security hygiene.

.ade

.adp

.app

.asp

.asa

.asnx

.asmx

.bas

.bat

.cdx

.cer

.chm

.class

.cmd

.com

.config

.cpl

.crt

.csh

.der

.dll

.docm

.dotm

.exe

.fxp

.gadget

.hlp

.hta

.htr

.htw

.ida

.idc

.idq

.inf

.ins

.isp

.its

.jar

.js

.jse

.ksh

.lib

.lnk

.mad

.maf

.mag

.mam

.maq

.mar

.mas

.mat

.mau

.mav

.maw

.mda

.mdb

.mde

.mdt

.mdw

.mdz

.msc

.msh

.msh1

.msh1xml

.msh2

.msh2xml

.mshxml

.msi

.msp

.mst

.ops

.pcd

.pif

.plg

.potm

.ppam

.ppsm

.pptm

.prf

.prg

.printer

.ps1

.ps1xml

.ps2

.ps2xml

.psc1

.psc2

.pst

.reg

.rem

.scf

.scr

.sct

.sh

.shb

.shs

.shtm

.shtml

.sldm

.soap

.stm

.tmp

.url

.vb

.vbe

.vbs

.vsmacros

.vsw

.ws

.wsc

.wsf

.wsh

.xlam

.xlm

.xltm

.xnk

.xlsm

 

 

 

Example Email

 

Need additional help? Submit a ticket with the Service Desk here: IT Service Desk Help Center

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Where to Download/Log In

outlook.com/seattleu.edu

Related Services

Accounts, Email

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