Slow sending of messages with attachments

Hello!

I have two Exchange 2013 servers. The first one is Mailbox and the second one is CAS.

There is no any problems if I send any messages inside the organization. Also, everything is OK if I send emails outside with attachments less than 10M(approximately). But if I try to send message with large attachment(20M for example) outside my organization it will be delivered after about 8 hours!

PS C:\Users\andrew> Get-Message -Filter {FromAddress -like "*@domain.org"}  | fl

Subject                         : test
InternetMessageId               : <2894B1FD-8317-49C9-B538-7331F3F293F1@tversu.ru>
FromAddress                     : andrew@domain.org
Status                          : Active
Size                            : 13.49 MB (14,142,047 bytes)
MessageSourceName               : SMTP:Default EX2013MBX01
SourceIP                        : 0:0:4e41:21::12
SCL                             : -1
DateReceived                    : 4/3/2016 12:30:26 PM
ExpirationTime                  : 4/5/2016 12:30:26 PM
LastError                       :
RetryCount                      : 0
Recipients                      : {andrew.zhukov@outside-domain.com;2;2;[{LRT=};{LED=};{FQDN=};{IP=}];0;CN=To
                                  Internet,CN=Connections,CN=Exchange Routing Group (DWBGZMFD01QNBJR),CN=Routing
                                  Groups,CN=Exchange Administrative Group (FYDIBOHF23SPDLT),CN=Administrative
                                  Groups,CN=Tver State University,CN=Microsoft
                                  Exchange,CN=Services,CN=Configuration,DC=domain,DC=org;0}
ComponentLatency                :
MessageLatency                  : 00:41:59.5558835
DeferReason                     : None
LockReason                      :
Priority                        : Low
ExternalDirectoryOrganizationId : 00000000-0000-0000-0000-000000000000
Directionality                  : Originating
OriginalFromAddress             : andrew@domain.org
AccountForest                   : ad-domain.org
MessageIdentity                 : ex2013mbx01\Submission\4294967310
Queue                           : ex2013mbx01\Submission
Identity                        : ex2013mbx01\Submission\4294967310
IsValid                         : True
ObjectState                     : New

PS C:\Users\andrew> get-transportconfig | ft maxsendsize, maxreceivesize

MaxSendSize                                                 MaxReceiveSize
-----------                                                 --------------
50 MB (52,428,800 bytes)                                    50 MB (52,428,800 bytes)


PS C:\Users\andrew> get-receiveconnector | ft name, maxmessagesize

Name                                                        MaxMessageSize
----                                                        --------------
Default EX2013MBX01                                         50 MB (52,428,800 bytes)
Client Proxy EX2013MBX01                                    50 MB (52,428,800 bytes)
Default Frontend EX2013CAS01                                50 MB (52,428,800 bytes)
Outbound Proxy Frontend EX2013CAS01                         50 MB (52,428,800 bytes)
Client Frontend EX2013CAS01                                 50 MB (52,428,800 bytes)
Client PlainText EX2013CAS01                                50 MB (52,428,800 bytes)


PS C:\Users\andrew> get-sendconnector | ft name, maxmessagesize

Name                                                        MaxMessageSize
----                                                        --------------
tversu.net                                                  Unlimited
To Internet                                                 50 MB (52,428,800 bytes)


PS C:\Users\andrew> get-mailbox andrew |ft Name, Maxsendsize, maxreceivesize

Name                                    MaxSendSize                             MaxReceiveSize
----                                    -----------                             --------------
andrew                                  Unlimited                               Unlimited

What you can advice to solve this problem?