在「phpBB 3.3.10 Release」這邊看到這個修正，研究了一下發現原來有些故事在後面跑：
Update the emoji CDN: PHPBB3-17071
Twitter Emoji (Twemoji) 這個計畫是 Twitter 弄出來的 open source project，最主要是讓不支援新版 Unicode 的系統上可以改用圖片顯示出來 (畢竟 Unicode 一直在加字)。
其中提供的 url 是 https://twemoji.maxcdn.com/v/latest/twemoji.min.js，可以看到裡面帶有 MaxCDN 的資訊，算是一種廣告，但後來 StackPath 在 2016 併購 MaxCDN，接下來是在去年打算要淘汰掉 MaxCDN 這個產品線：「MaxCDN and SecureCDN are Retiring; Here’s What It Means for You」。
這件事情被帶到「Clarify MaxCDN URLs now that MaxCDN is retiring #556」這邊討論，但看起來沒有太多動作，後來在「Maxcdn has shut down, cdn not working anymore. #580」這邊又被帶起來討論，其中 Twitter 前員工大概提了一下情況，主要是當年他們跟 MaxCDN 有談過讓 MaxCDN 負責頻寬的部份：
@simplexx among all the things, twemoji has always been a Twitter service for the community.
At my times in there, we had a great agreement / deal with MaxCDN so that it's hard to blame the boss this time, as MaxCDN is a completely different company/story.
What I see is some poor attention to this project, as companies don't close from a day to another (usually?) but as we all know what's going on @ twitter, I can't really blame any of my former colleagues, or new arrivals there.
Please let's not make it a wall of shame for all the people that worked on this, thanks for your understanding (I've left 7 years ago or more, as example, I've got pinged by some follower and I'm just trying to help you out anyway).
另外也有人提到目前 Twitter 的溝通管道的狀況：
For what it's worth, while I was still there we were in talks with MaxCDN to have the same deal when they migrated to be Stackpath. Everyone who had worked on the deal with MaxCDN had left and left no record of that deal, so it was taking them a bit longer to work out than expected – MaxCDN used to offer free hosting to OSS projects, but Stackpath wouldn't be doing that. They were working on an exception for us, but any emails they send to our Twitter emails now get bounced, so I guess they could've gotten this sorted out before shutting down MaxCDN... but it's not like we're there on the other end to make it happen, so it appears we'll never know.
Anyway，現在是至少讓 twemoji.maxcdn.com 恢復到「會動」了，但情況變得很特殊，twemoji.maxcdn.com 這個網址目前是指到競業的 BunnyCDN 上：
;; ANSWER SECTION: twemoji.maxcdn.com. 229 IN CNAME twemoji.b-cdn.net. twemoji.b-cdn.net. 35 IN A 23.248.177.58
但如果你真的打過去要檔案，會是 301 到 jsDelivr 上：
$ http https://twemoji.maxcdn.com/2/svg/1f525.svg [...] Location: https://cdn.jsdelivr.net/npm/twemoji@11.3.0/2/svg/1f525.svg [...]
而 jsDelivr 目前是放在 Fastly 上：
;; ANSWER SECTION: cdn.jsdelivr.net. 180 IN CNAME jsdelivr.map.fastly.net. jsdelivr.map.fastly.net. 30 IN A 199.232.45.229
但在 GitHub 的說明上面則是建議用 UNPKG：
<script src="https://unpkg.com/twemoji@latest/dist/twemoji.min.js" crossorigin="anonymous"></script>
而 UNPKG 目前的 CDN 的部份則是 Cloudflare：
;; ANSWER SECTION: unpkg.com. 86400 IN NS anirban.ns.cloudflare.com. unpkg.com. 86400 IN NS aron.ns.cloudflare.com.
;; ANSWER SECTION: unpkg.com. 300 IN A 104.16.126.175 unpkg.com. 300 IN A 104.16.123.175 unpkg.com. 300 IN A 104.16.122.175 unpkg.com. 300 IN A 104.16.124.175 unpkg.com. 300 IN A 104.16.125.175
指到 BunnyCDN 但是 BunnyCDN 只負責 redirect，然後也不是導到 UNPKG 上...