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MAKING SENSE OF EMAIL
PART 1: ATTACHMENT DISORDERS
by Richard Phillips |
Reliably sending, receiving and using eMail attachments can sometimes seem as much like magic as it does science. One attachment goes through to the recipient while another does not and we are left trying to fathom why the difference. In about ten minutes (the time it’ll take to read this), you'll learn how to solve this mystery.
WHY WAS MY
ATTACHMENT BLOCKED?
Reason One: Virus Concerns
Anyone running a Windows PC knows the serious threat presented by viruses, spyware and the like. Some of these software nasties can and do arrive in the form of eMail attachments. Most ISPs (Internet Service Providers) are aware of this and as such some have setup their mail servers to scan incoming messages for known viruses. Furthermore, many individual users are running programs that automatically check incoming eMail for known viruses. In either case if an attachment is discovered to be infected, it is instantly deleted.
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Article Summary:
To improve the odds of your attachments making it to the intended recipient...
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Confirm that your PC is free of viruses and other software infections. |
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Keep the total size of your outgoing eMail (including any attachments) below five or ten megabytes. |
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When attaching certain files to an outgoing eMail it might be wise to first compress the files using a ZIP utility. |
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Include unique descriptive text in your eMail’s subject line and body area so that the recipient can be certain the message really comes from you. |
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Most of us probably won’t object to this. After all, we certainly don’t want to pass along a nasty bug to clients and coworkers. The downside to this method, however, is that a security scanning program can only alert you to a contagion if it has been programmed to look for it. As a result brand spanking new viruses will slip through the net.
To combat this potential flaw, some security software can scan every attachment for executable code. Calling something an “executable” is just another way of saying that it can run on a computer (like a program). There are good executables such as your word processor or your eMail program. And there are bad executables such as spyware. If executable code is discovered in your attachment, regardless of whether or not the code is of the infectious variety, the attachment (or possibly your entire message) may be deleted. And note that executable code can reside in all kinds of files, not just those with the ‘.exe’ file extension.
What’s worse some seemingly innocent files such as bitmapped (‘.bmp’) and JPEG (‘.jpg’) graphics files can be rigged in such a way as to cause what is known as a “buffer overrun.” This little trick can cause a file that doesn’t seem to contain anything bad to morph into a nasty little bugger that is all to happy to eat your computer for lunch. To fight back, some security software may be blocking these kinds of attachments as well. Considering the business many of you are in, I’ll bet the need to send JPEG attachments is a fairly common occurrence.
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‘Virus Concerns’ Solution
I know this seems obvious but keep your computer free of infection. An eMail attachment that isn’t carrying the software equivalent of the plague is far less likely to be rejected by an ISP’s mail server or by the user’s security software.
There are several excellent (free) spyware and virus scanning utilities available. If there is interest I will gladly publish a list of these software utilities in a future newsletter.
By the way, for the moment this is a Windows only issue. As I write this there are no spyware or virus issues on the Macintosh. |
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WHY WAS MY
ATTACHMENT BLOCKED?
Reason Two: Server Limits
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Most eMail accounts have size limits placed on them. These limits control the maximum size of incoming and outgoing eMail. It also limits the combined size of all the messages that are stored on the mail server. As an example, Google’s Gmail service provides each user with over two–gigabytes (2GB) of online mail storage. And yet even with all that storage space, no single eMail sent to someone with a Gmail account can exceed ten–megabytes (10MB) in size.
I’ve noticed that on average most services limit each eMail message to around five or ten megabytes (however, I’ve seen some with a ceiling as low as one–megabyte).
When composing a message it’s important to remember that the total size of your eMail will include all of the files you’ve attached plus the actual message text. But here’s the real gotcha:
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Files tend to get larger when they
are attached to an eMail.
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That’s right! Simply attaching a file to your outgoing eMail can cause the size of the attached file to grow. Sometimes the expansion is slight. Sometimes it’s great. Worst case scenario: it is possible for an attached file to grow to nearly double its original size (although on average the attachment process will force a file’s data to require about 1.5 times the space of the original).
Let’s say you have a four–megabyte (4MB) Photoshop file that you want to attach to an outgoing message. The intended recipient of this eMail has a five–megabyte ceiling on his or her mail account. No problem, right? Maybe. But the odds are that the expanded Photoshop file is going to grow beyond the limits of the recipient’s mailbox. This means your eMail will be rejected.
I experimented with an average Photoshop file that weighed in at just over four–megabytes. As an eMail attachment this file ballooned up to just under five–point–five–megabytes (5.5MB).
Please note that when attaching a file to an outgoing eMail, the original file itself doesn’t grow or change. But rather it is the amount of space required to send the attached file that can expand.
Also note that when the recipient of your attachment extracts the file from your eMail then their copy will be restored to its original and proper size.
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‘Server Limits’ Solution
Keep the total size of your eMail below ten-megabytes (10MB). Or if possible, play it safer and keep it below five-megabytes (5MB) (remember to multiply the size of each attached file by 1.5 for a “real world” size guesstimate).
If you wish to transfer several files to someone then you might consider sending multiple eMail messages to the recipient with each message carrying just a few attached files. But remember that many mail accounts also have a maximum total eMail storage limit. Although with most services the total storage area size limit is usually quite a bit larger than the per–message size limit. |
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SOMETHING ELSE TO CONSIDER:
File Compression
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A great way to work around many of these roadblocks is to first compress the file (or files) into a single ZIP archive and then attach the archived file to your outgoing eMail.*
This method does require an extra step before sending the eMail (creating the archive file) and that the recipient also perform an extra step after receiving the eMail (decompressing the archive file). So it may not be an ideal solution for some. However, if you are routinely having trouble sending or receiving attachments to/from a specific person, it might be worth a shot. This method also requires that the recipient of your eMail have an unzipping utility.
A big plus to using compression is that you increase the chances of staying under the mail server’s “the eMail is too big” limit. Also, ZIP files tend not to be seen by most security scanning software as something that is bad.
Please note that very little reduction in size will be achieved by compressing movie files and JPEGs. This is because these kinds of files are already heavily compressed. Even so, ZIPping such files might allow them to more easily slip by an ISPs scanning software.
There are many free and inexpensive ZIP utilities available on VersionTracker.com and Downloads.com |
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Please note that this compression technique will not work if you are sending eMail to a Google Gmail user and your ZIPped attachment file contains an executable program. In such a situation Gmail will block the message even if the program embedded in the attached ZIP file is harmless. Furthermore, it is possible that other eMail services are doing this as well (or soon will be). |
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THE SAFEST WAY TO USE
EMAIL ATTACHMENTS?
DON’T!
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Most security experts believe (and I agree) that it is best to avoid sending or opening received eMail attachments. Why? Because attachments are a favorite way for the bad guys to move infectious programming code from one computer to another. And just because an eMail seems to come from someone you know doesn’t mean the attachment is safe. There are tricks viruses can use to deceive you into thinking that the innocent looking but infected eMail attachment you just received is coming from a friend.
Okay, that’s the recommendation. But here on planet Earth we know there are times when we have to attach files to our eMails. The question then becomes what can the sender do to help the person who will receive your eMail know that the attachment really came from you and isn’t simply something kicked out by a virus? |
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Don’t
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simply add an attachment to an otherwise blank eMail and then send the eMail without first adding some kind of descriptive text. Preferably, descriptive text should be typed into both the message’s subject line and the body of the message.
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Don’t
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add subject line or message body text that is too generic. In other words, avoid writing something like, “here are the files you wanted” or “this contains the data you’ve been waiting for.”
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Why?
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Because when viruses create their infection laden eMails they will very often send them with either no body text at all, or optionally they may include a very generic message. Consider how a received eMail attachment with the explanatory text that reads something like “I know you’ve been waiting for this” will seem quite ordinary in almost any imaginable situation. This is one trick virus writers use to slip their evil creations past the smartest part of any security plan: the human running the computer.
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Do
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add enough uniquely descriptive text to your outgoing eMail so that the recipient will know for certain that your attachment is legitimate. For example include something detailed like, “Jane, here are the JPEGs for the June ‘Kwik-E-Mart’ brochure. -Bill Notfaux”
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Why?
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Because (at least for the moment) viruses aren’t smart enough to add that level of identifying information to an eMail. Therefore, when you add unique and detailed information then you’ve helped the recipient to identify the eMail as coming from a flesh and blood person rather than a chunk of software.
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Caveat:
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Sadly none of these suggestions will guarantee the protection of a PC if the user opens an attachment where the computer that originated the eMail is infected.
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Congratulations! You’ve just taken a big step to making sure that attachments will never again get the better of you.
In a future issue of SP News we’ll tackle the other half of the eMail attachment issue: why can’t we open one another’s files?
Questions, comments, problems, please let me know. |
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Miracle Max: Don't rush me sonny. You rush a miracle man, you get rotten miracles. |
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