In /usr/local/share/pear/Horde/Mapi.php line 172 a Math_BigInteger object is instantiated: 172 $bci = new Math_BigInteger('0'); However, mail/pear-Horde_Mapi does not depend on pear-Math_BigInteger. Please add a dependency on pear-Math_BigInteger.
A commit references this bug: Author: mm Date: Wed Jun 8 21:29:15 UTC 2016 New revision: 416566 URL: https://svnweb.freebsd.org/changeset/ports/416566 Log: Depend pear-Horde_Mapi on pear-Math_BigInteger PR: 210123 Changes: head/mail/pear-Horde_Mapi/Makefile
I have also submitted bug #210151 to update pear-Math_BigInteger to 1.0.3