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YMac, IT Specialist
Category: Mac
Satisfied Customers: 60
Experience:  I have been using Macs for 20 years and have 10 years experience in IT.
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We have a G4 imac powerpc with OS 10.4.11; we use Comcast as

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We have a G4 imac powerpc with OS 10.4.11; we use Comcast as our internet provider. About two weeks ago we were suddenly unable to send any e-mails that had attachments and we are unable to upload attachments to a school website. We also have problems logging in to some online accounts. After several calls and hours with Comcast, they say there's something wrong with the computer, not the Comcast settings. We've gone to to test our connections; it will do the download test fine, but it stops when it attempts the upload test. Please help us if you can! Thanks so much.
Are you connected to the internet through a router or directly to the modem.
What model modem/router do you have.

It possibly could be an MTU size issue.

Let me know.
Customer: replied 7 years ago.
We are connected directly to the modem; it's the one supplied by Comcast 4 years ago, made by Scientific-Atlanta. We cannot even send an Word attachment of 30k; a download speed test today on one site showed our download speed for their particular test at only 6kbps!

(This is my 4th try trying to upload this response; after several minutes I get a page load error).
Do you have another computer you can try and connect to the modem to see if the same issue occurs? That would help ruling out the computer as the problem or confirming that it is an issue with the machine itself.

You can also try restarting your imac in safe mode to repair issues that the machine might be having. Here's Apples documentation on doing that:

Try the above 2 suggestions and let me know your findings.
Also to clarify. If you send an email without an attachment it goes through without a problem correct?

Customer: replied 7 years ago.
Thanks again for trying to help us. We only have one computer, so we can't try to connect the modem to another. After restarting in safe mode, nothing was improved or changed.

Yes, we can send e-mail without attachments with no problem.
-How big is the attachment you are trying to send? Comcast has a limit of about 10MB (15 including email header)
-Do you get any error message in your email client when you try to send (if you do please include the full error message in your response)
-Try sending a very small attachment. (start a text file and write one word in it, attach it to your email and try sending that)
- look in your outbox, are there any emails sitting in the outbox that have not been sent? If yes, delete messages > close your email client > restart the email client and try sending again.

Let me know what how those tests go.
Also would you please post your email client settings?
especially your smtp settings.

Customer: replied 7 years ago.
The largest attachments we've been trying to send recently are all small Word documents of 30-40k. In the past I've sent documents as large as 5MB.
Error message from email says "Cannot send message using the server The server response was: An error occurred while delivering this message via the SMTP server "(null)" Use the pop-up menu below to try a different outgoing mail server. All messages will use this server until you quit Mail or change your network settings."
The one-word document attachment did not work. The only emails in the outbox have been two or three 30k word documents attached to test emails. They have been deleted, Mail restarted, and the problem remains. (Same error message).
Outgoing Mail Server:
Server port: 587
Use Secure Sockets Layer (SSL) is checked.
Authentication: Password
User Name and Password XXXXX filled out.
Comcast techs had us change the Server port number and change the authentication from none to password.

Please don't forget that we also have the uploading problem to various websites as well. Even this reply message will likely take several attempts.
I really suspect the modem is the issue, but I was trying to rule out issues on your system itself.
Do you have any other problems on your machine that are not network related. For example if you run applications that aren't networked does the machine run slow or have any other type of issues.

I've seen that type of problem solved by lowering the MTU size on the router or modem, but I'm not sure your modem is manageable and that this setting can be modified, if you post the exact model number I can check it out.

Also what I would personally do is call Comcast and request them to send you a new modem. 4 years is very old in a technology realm, and if nothing else modems today are lot more performing.

If they refuse you could also get your own modem from any electronics store, but I doubt they will refuse. I've successfully gotten different ISPs to replace my modem on a couple of occasions.
YMac and other Mac Specialists are ready to help you
Customer: replied 7 years ago.
I called Comcast to request a new modem; they sent me to a local office 10 minutes away to pick up a new modem. It's installed and I can now send attachments again, and the website I couldn't log into is now working. Also, the site and internet frog test site could both load properly and completed the tests properly, showing good download and upload times.

I just wish Comcast would have suggested this more than a week ago when we started having problems.

I appreciate your time and effort in resolving this for us.