Often the most famous generic URL shorteners get blacklisted. If you send an email containing links shortened with generic, common domains that are blacklisted, your email will probably end up in the spam (abuse) folder of your audience.

Why does this happen, though? Generic domains are used by millions of people, including spammers to share malware, phishing content and any sort of illegal stuff. Anyone can create an account and create his short link for free and it’s really difficult to check every single link that has been created.

SURBL maintains an updated list of the top 10 most abused URL shorteners (Blacklisted).
Following the list updated Aug, 22, 2020:

1.	bit.ly
2.	bit.do
3.	ow.ly
4.	goo.gl
5.	x.co
6.	rebrand.ly
7.	tinyurl.com
8.	t.co
9.	is.gd
10.	ht.ly

The solution to this problem is to shorten your URLs using your custom domain name as a redirector. In this way, only you are able to create links with that domain and, unless you are a spammer, you won’t be blacklisted.

Also you may want to take a loot at the most abusive TLD’s to avoid using them for redirects and/or your primary wesbite (.com here is just before it have the most registrations – so it’s not the rule):

Below are the top 20 TLDs listed in SURBL (unique counts).
Numbers on the left are counts of the domains in the TLDs on the right:

185591 com
46330 work
37474 xyz
25346 top
21889 site
20419 net
19167 live
18833 cn
15347 icu
15250 wang
10072 fit
9502 vip
9258 ru
8628 life
6342 cam
6117 us
5649 rest
4442 biz
4370 co
4192 agency