diff --git a/go.mod b/go.mod
index bf576a0..ac464b2 100644
--- a/go.mod
+++ b/go.mod
@@ -21,7 +21,7 @@ require (
 	github.com/jordan-wright/email v4.0.1-0.20210109023952-943e75fe5223+incompatible
 	github.com/kr/text v0.2.0 // indirect
 	github.com/line/line-bot-sdk-go v7.8.0+incompatible
-	github.com/mailgun/mailgun-go/v4 v4.4.1
+	github.com/mailgun/mailgun-go/v4 v4.5.1
 	github.com/mattn/go-colorable v0.1.8 // indirect
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.1 // indirect
diff --git a/go.sum b/go.sum
index 1a32b86..fdf8ced 100644
--- a/go.sum
+++ b/go.sum
@@ -129,8 +129,8 @@ github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
 github.com/line/line-bot-sdk-go v7.8.0+incompatible h1:Uf9/OxV0zCVfqyvwZPH8CrdiHXXmMRa/L91G3btQblQ=
 github.com/line/line-bot-sdk-go v7.8.0+incompatible/go.mod h1:0RjLjJEAU/3GIcHkC3av6O4jInAbt25nnZVmOFUgDBg=
-github.com/mailgun/mailgun-go/v4 v4.4.1 h1:b58b7a5QZSTkfaE89OeN0dXzcY+HyJXOfalvuSDL1Q8=
-github.com/mailgun/mailgun-go/v4 v4.4.1/go.mod h1:FJlF9rI5cQT+mrwujtJjPMbIVy3Ebor9bKTVsJ0QU40=
+github.com/mailgun/mailgun-go/v4 v4.5.1 h1:XrQQ/ZgqFvINRKy+eBqowLl7k3pQO6OCLpKphliMOFs=
+github.com/mailgun/mailgun-go/v4 v4.5.1/go.mod h1:FJlF9rI5cQT+mrwujtJjPMbIVy3Ebor9bKTVsJ0QU40=
 github.com/mattn/go-colorable v0.1.1/go.mod h1:FuOcm+DKB9mbwrcAfNl7/TZVBZ6rcnceauSikq3lYCQ=
 github.com/mattn/go-colorable v0.1.8 h1:c1ghPdyEDarC70ftn0y+A/Ee++9zz8ljHG1b13eJ0s8=
 github.com/mattn/go-colorable v0.1.8/go.mod h1:u6P/XSegPjTcexA+o6vUJrdnUu04hMope9wVRipJSqc=