I have two customers who can't send me pdf attachments larger than 100kb without them failing or being delayed up to 24hours. Everyone else can send the same or larger attachments through just fine.
Things I have tried to fix the problem :
Disable spam filtering
Disable tarpitting
increase timeout to 2:30:00
Verify MTU is set correctly
Whitelist the IP Address of the sender
Some logs of a file that didn't go through:
2016-01-25T21:37:47.387Z,EXCHANGE01\Default EXCHANGE01,address,0,10.0.1.19:25,x.x.x.x:60062,+,,
2016-01-25T21:37:47.387Z,EXCHANGE01\Default EXCHANGE01,address,1,10.0.1.19:25,x.x.x.x:60062,*,SMTPSubmit SMTPAcceptAnySender SMTPAcceptAuthoritativeDomainSender AcceptRoutingHeaders,Set Session Permissions
2016-01-25T21:37:47.402Z,EXCHANGE01\Default EXCHANGE01,address,2,10.0.1.19:25,x.x.x.x:60062,>,"220 exchange01.domain.local Microsoft ESMTP MAIL Service ready at Mon, 25 Jan 2016 15:37:46 -0600",
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,3,10.0.1.19:25,x.x.x.x:60062,<,EHLO Zixserver,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,4,10.0.1.19:25,x.x.x.x:60062,>,250-exchange01.domain.local Hello [x.x.x.x],
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,5,10.0.1.19:25,x.x.x.x:60062,>,250-SIZE,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,6,10.0.1.19:25,x.x.x.x:60062,>,250-PIPELINING,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,7,10.0.1.19:25,x.x.x.x:60062,>,250-DSN,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,8,10.0.1.19:25,x.x.x.x:60062,>,250-ENHANCEDSTATUSCODES,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,9,10.0.1.19:25,x.x.x.x:60062,>,250-STARTTLS,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,10,10.0.1.19:25,x.x.x.x:60062,>,250-X-ANONYMOUSTLS,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,11,10.0.1.19:25,x.x.x.x:60062,>,250-AUTH NTLM,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,12,10.0.1.19:25,x.x.x.x:60062,>,250-X-EXPS GSSAPI NTLM,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,13,10.0.1.19:25,x.x.x.x:60062,>,250-8BITMIME,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,14,10.0.1.19:25,x.x.x.x:60062,>,250-BINARYMIME,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,15,10.0.1.19:25,x.x.x.x:60062,>,250-CHUNKING,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,16,10.0.1.19:25,x.x.x.x:60062,>,250-XEXCH50,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,17,10.0.1.19:25,x.x.x.x:60062,>,250-XRDST,
2016-01-25T21:37:47.434Z,EXCHANGE01\Default EXCHANGE01,address,18,10.0.1.19:25,x.x.x.x:60062,>,250 XSHADOW,
2016-01-25T21:37:47.465Z,EXCHANGE01\Default EXCHANGE01,address,19,10.0.1.19:25,x.x.x.x:60062,<,STARTTLS,
2016-01-25T21:37:47.465Z,EXCHANGE01\Default EXCHANGE01,address,20,10.0.1.19:25,x.x.x.x:60062,>,220 2.0.0 SMTP server ready,
2016-01-25T21:37:47.465Z,EXCHANGE01\Default EXCHANGE01,address,21,10.0.1.19:25,x.x.x.x:60062,*,,Sending certificate
2016-01-25T21:37:47.465Z,EXCHANGE01\Default EXCHANGE01,address,22,10.0.1.19:25,x.x.x.x:60062,*,CN=exchange01,Certificate subject
2016-01-25T21:37:47.465Z,EXCHANGE01\Default EXCHANGE01,address,23,10.0.1.19:25,x.x.x.x:60062,*,CN=exchange01,Certificate issuer name
2016-01-25T21:37:47.465Z,EXCHANGE01\Default EXCHANGE01,address,24,10.0.1.19:25,x.x.x.x:60062,*,****,Certificate serial number
2016-01-25T21:37:47.465Z,EXCHANGE01\Default EXCHANGE01,address,25,10.0.1.19:25,x.x.x.x:60062,*,****,Certificate thumbprint
2016-01-25T21:37:47.465Z,EXCHANGE01\Default EXCHANGE01,address,26,10.0.1.19:25,x.x.x.x:60062,*,exchange01;exchange01.domain.local,Certificate alternate names
2016-01-25T21:37:47.543Z,EXCHANGE01\Default EXCHANGE01,address,27,10.0.1.19:25,x.x.x.x:60062,*,,"TLS protocol SP_PROT_TLS1_0_SERVER negotiation succeeded using bulk encryption algorithm CALG_AES_128 with strength 128 bits, MAC hash algorithm CALG_SHA1 with strength 160 bits and key exchange algorithm CALG_RSA_KEYX with strength 2048 bits"
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,28,10.0.1.19:25,x.x.x.x:60062,<,EHLO server,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,29,10.0.1.19:25,x.x.x.x:60062,*,,TlsDomainCapabilities='None'; Status='NoRemoteCertificate'
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,30,10.0.1.19:25,x.x.x.x:60062,>,250-exchange01.domain.local Hello [x.x.x.x],
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,31,10.0.1.19:25,x.x.x.x:60062,>,250-SIZE,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,32,10.0.1.19:25,x.x.x.x:60062,>,250-PIPELINING,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,33,10.0.1.19:25,x.x.x.x:60062,>,250-DSN,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,34,10.0.1.19:25,x.x.x.x:60062,>,250-ENHANCEDSTATUSCODES,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,35,10.0.1.19:25,x.x.x.x:60062,>,250-AUTH NTLM LOGIN,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,36,10.0.1.19:25,x.x.x.x:60062,>,250-X-EXPS GSSAPI NTLM,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,37,10.0.1.19:25,x.x.x.x:60062,>,250-8BITMIME,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,38,10.0.1.19:25,x.x.x.x:60062,>,250-BINARYMIME,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,39,10.0.1.19:25,x.x.x.x:60062,>,250-CHUNKING,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,40,10.0.1.19:25,x.x.x.x:60062,>,250-XEXCH50,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,41,10.0.1.19:25,x.x.x.x:60062,>,250-XRDST,
2016-01-25T21:37:47.574Z,EXCHANGE01\Default EXCHANGE01,address,42,10.0.1.19:25,x.x.x.x:60062,>,250 XSHADOW,
2016-01-25T21:37:47.605Z,EXCHANGE01\Default EXCHANGE01,address,43,10.0.1.19:25,x.x.x.x:60062,<,MAIL FROM:<****> SIZE=278779,
2016-01-25T21:37:47.605Z,EXCHANGE01\Default EXCHANGE01,address,44,10.0.1.19:25,x.x.x.x:60062,*,address;2016-01-25T21:37:47.387Z;1,receiving message
2016-01-25T21:37:47.605Z,EXCHANGE01\Default EXCHANGE01,address,45,10.0.1.19:25,x.x.x.x:60062,<,RCPT TO:<recipient@domain.net> ORCPT=rfc822;*****@*****,
2016-01-25T21:37:47.605Z,EXCHANGE01\Default EXCHANGE01,address,46,10.0.1.19:25,x.x.x.x:60062,<,DATA,
2016-01-25T21:37:47.605Z,EXCHANGE01\Default EXCHANGE01,address,47,10.0.1.19:25,x.x.x.x:60062,>,250 2.1.0 Sender OK,
2016-01-25T21:37:47.605Z,EXCHANGE01\Default EXCHANGE01,address,48,10.0.1.19:25,x.x.x.x:60062,>,250 2.1.5 Recipient OK,
2016-01-25T21:37:47.605Z,EXCHANGE01\Default EXCHANGE01,address,49,10.0.1.19:25,x.x.x.x:60062,>,354 Start mail input; end with <CRLF>.<CRLF>,
2016-01-25T21:37:47.683Z,EXCHANGE01\Default EXCHANGE01,address,50,10.0.1.19:25,x.x.x.x:60062,-,,Remote