I used an online tracerotue tool located at http://www.infosyssec.com/infosyssec/ipsectools.htm.
When I trace route to their servers, I get:
1?: [LOCALHOST] pmtu 1500
1?: cisco.ceti.com.pl (195.116.211.1)
2?: ceti-gw.cyfronet.krakow.pl (195.150.0.149)
3?: 195.94.194.145 (195.94.194.145)
4?: waw-p2r1-atm1-0-4.ipartners.pl (217.153.2.193)
5?: debln302-tc-p0-1.ebone.net (195.158.246.133) asymm 6
6?: debln301-tc-p5-0.ebone.net (213.174.70.37) asymm 5
7?: dedus206-tc-p6-0.ebone.net (213.174.70.41) asymm 17
8?: defra228-tc-p1-0.ebone.net (213.174.70.130) asymm 16
9?: defra228-tc-p1-0.ebone.net (213.174.70.130) asymm 16
10?: defra229-tc-p5-0.ebone.net (213.174.70.22) asymm 15
11?: frpar308-tc-p2-0.ebone.net (213.174.70.214) asymm 14
12?: gblon523-tc-p8-0.ebone.net (213.174.71.65)
13?: gblon504-tc-r10-0.ebone.net (213.174.68.241) asymm 11
14?: gblon303-tc-p2-0.ebone.net (213.174.70.94) asymm 10
15?: gblon303-tc-p2-0.ebone.net (213.174.70.94) asymm 10
16?: gblon304-tb-p2-0.ebone.net (195.158.225.30) asymm 11
17?: zpr1-sonet2-0-0-0.Londonlnt.cw.net (195.10.35.97) asymm 18
17?: bcr2-so-2-0-0.Thamesside.cw.net (166.63.209.197) asymm 16
17?: zcr1-ge-2-1-0.Londonlnt.cw.net (195.10.7.193)
18?: dcr2-loopback.Washingtondck.cw.net (206.24.226.100) asymm 14
18?: dcr2-loopback.Washingtondck.cw.net (206.24.226.100) asymm 14
19?: agr4-so-2-0-0.Washingtondck.cw.net (206.24.238.190) asymm 14
19?: agr4-so-2-0-0.Washingtondck.cw.net (206.24.238.190) asymm 14
20?: acr1-loopback.Seattlesel.cw.net (208.172.82.61) asymm 13
20?: acr1-loopback.Seattlesel.cw.net (208.172.82.61) asymm 13
21?: ngcore1.Seattle.cw.net (204.70.9.129) asymm 14
21?: ngcore1.Seattle.cw.net (204.70.9.129) asymm 14
22?: microsoft-itg.Seattle.cw.net (166.49.26.74) asymm 17
23?: iuscixtukc1201-ge-5-0.msft.net (207.46.129.47) asymm 17
24?: iustixcpdc1201-p-3-0.msft.net (207.46.190.26) asymm 18
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Too many hops: pmtu 1500