DNS is not an issue as the problem PC's pick up the correct IP.
Optus does have problems with DNS problems with arbitrary domains all the time.
Is the PC you are testing from on Optus NBN?
Yes. The sites using Optus NBN cannot connect, while all other sites can.
Considering the Optus NBN sites that aren't working when attempting to contact the server return the correct IP, I didn't suspect DNS. I think for one site I changed the PC to use Google DNS (220.127.116.11) and still had the same issue, hence why I suspect an internal Optus routing issue.
Also, I don't mean to hijack this thread, this was merely me chiming in suspecting that the original post and my issues could be of a similar cause.
please do hijack this thread i have about a dozen sites on that server so its annoying to think anyone on optus nbn cant reach it, can't reach mail servers either.
Trying to chat with optus technical is a huge time waster im thinking of just moving my clients mailserver onto godaddy or some other cheap hosting until optus sorts this out.
Yes, I don't know how many users your mailserver has, but I found with a small number say up to 10 or 20, it was worth using hosted exchange at around $6-7/user/month.
In the meantime , a tracert will be most interesting when you are able to get onsite.
So if its a simple HTTPS connection and the domain resolves to an IP, if you go the the URL what kind of error do you get?
With all the people reporting these Optus NBN specific problems I've always been able to visit their domains without problem. I'm on Optus FTTC but don't use the Optus router and I user Cloudflare DNS.
I'm happy to check out a URL/domain or do a tracert if you need.
There are a couple of other tests I’m going to try out tomorrow. I’ll let you know what I find. Thanks 🙏
No problem. Can you find out if the client has this Optus modem at home. If they do it will be an interesting test to see if they can get to the site when the modem is in 4G backup mode.