Attachment links blocked by client firewalls

[Terrible Toll]

We have the 360works CloudMail plug-in employed to send batch emails to our participants. It uploads attachments to AWS and includes a download link on each email, however, some of our city clients are being blocked from accessing the attachments by their firewall.

We have the domains all fully certified and verified by AWS, so does anyone have any idea what could be the possible cause of this.

 

Thanks in advance, Anatole Beams

Edited January 11, 2019 by Terrible Toll
addition of example link

[Terrible Toll]

I think it may be because the initial link on the email to download the attachment is not secure. Example: http://54.91.242.137/CloudMail/click/49857fb6-3454-4b18-b3d8-a07a78a6f76f/0

Surely this should be a secure link? The IP address is the one supplied when CloudMail links to AWS, so I am not sure if we have any control over this.

Other CloudMail links such as unsubscribe are also similar so will likely have the same problem if clients are blocked from using insecure sites.

Edited January 11, 2019 by Terrible Toll

[Terrible Toll]

I have set up a subdomain on our domain so the link on the attachment is now:

http://aws.momentum.uk.com/CloudMail/click/49857fb6-3454-4b18-b3d8-a07a78a6f76f/0

However, this initial link off the email is insecure (http). It links in turn to secure location where the image is stored (https). 

Does anyone know if it is possible to make the intermediate link https as well? Why is it that the IP address that we have on AWS is only http?

Edited January 12, 2019 by Terrible Toll

[OlgerDiekstra]

How do you know a firewall is blocking the link? Generally, a firewall would allow port 80 traffic as it's pretty common. Any company blocking outbound port 80 or 443 will find themselves in trouble sooner or later.

It's probably more likely that they have a web content filtering system in use that blocks the link. In which case they just need to unblock (whitelist) the url aws.momentum.uk.com.

If it is a web content filter causing the issue, making it https will probably not do much as most will look at the url.

I can access the link fine.

Edited January 13, 2019 by OlgerDiekstra

[Terrible Toll]

Thanks for your response Olger. You could be quite right. I am not able to reproduce the problem, so it could be just a filter. However, I suspect it is not just the one client, which make me think it is more than just that.