It's not about the .online TLD being "weird". The problem is that it was free. That's going to attract a swarm of fraudsters, spammers, etc, and then turn into a strong "this is probably fraud" signal in all kinds of fraud scoring systems.

There are lots of domains out there other than .com that are just fine.

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fckgw 6 hours ago | parent | next [-]

.online, .top, .xyz. info and .shop are some of the top TLDs that scammers use, precisely because of their rock bottom registrar fees that make them attractive for sites that have a shelf life of a few hours or a few days before being blocked. As a result, many places have a blanket "suspicious" flag for fresh domains under these TLDs.

If you plan on building a legit site, do not use any of these cheap TLDs.

	▲	al_borland 6 hours ago \| parent [-]
		Paying through the nose for a .com that is remotely memorable and easy to spell is not a great path forward for a hobbyist or someone who simply wants their own domain for email. I know someone with a .org domain, and even they have a ton of issues with false flags on their emails due to not coming from a big email provider. They’ve been blacklisted a couple times and regularly get flagged as spam. I’m surprised he hasn’t given up after dealing with this stuff for 25 years. These new TLDs, I thought, were supposed to open up more options for regular people to get a domain that is semi-decent. Instead they’re essentially useless. Some of the prices are also still insane, due to assumed “premium” status or domain squatters. There has to be a better way to police this stuff.

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garganzol 6 hours ago | parent | prev [-]

Probably this is what's happened here. Either the OP's domain was previously used for shady activities, or the almost-free stigma puts the whole .TLD in the grey list of high-risk assets. Probably is also explains the nuclear behavior of the registrar (suspension).

Free is good, but sometimes it's not.